rename the SingleTest class and and Java doc. make errors="" actually set to null to be more clear.

runtime-testsuite/test/org/antlr/v4/test/runtime/BaseRuntimeTest.java

@@ -23,6 +23,14 @@ import java.util.List;
 import static junit.framework.TestCase.assertEquals;
 import static org.junit.Assume.assumeFalse;
 
+/** This class represents a single runtime test. It pulls data from
+ *  a {@link RuntimeTestDescriptor} and uses junit to trigger a test.
+ *  The only functionality needed to execute a test is defined in
+ *  {@link RuntimeTestSupport}. All of the various test rig classes
+ *  derived from this one. E.g., see {@link org.antlr.v4.test.runtime.java.TestParserExec}.
+ *
+ *  @since 4.6.
+ */
 public abstract class BaseRuntimeTest {
 	public final static String[] Targets = {
 		"Cpp",
@@ -36,10 +44,10 @@ public abstract class BaseRuntimeTest {
 		"Node", "Safari", "Firefox", "Explorer", "Chrome"
 	};
 
-	protected SingleTest delegate;
+	protected RuntimeTestSupport delegate;
 	protected RuntimeTestDescriptor descriptor;
 
-	public BaseRuntimeTest(RuntimeTestDescriptor descriptor, SingleTest delegate) {
+	public BaseRuntimeTest(RuntimeTestDescriptor descriptor, RuntimeTestSupport delegate) {
 		this.descriptor = descriptor;
 		this.delegate = delegate;
 	}

runtime-testsuite/test/org/antlr/v4/test/runtime/BaseRuntimeTestDescriptor.java

@@ -8,6 +8,12 @@ import java.util.List;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+/** An abstract but mostly complete test descriptor that pulls values
+ *  for the various runtime test descriptor methods such as {@link #getInput()}
+ *  from fields using reflection.
+ *
+ *  @since 4.6
+ */
 public abstract class BaseRuntimeTestDescriptor implements RuntimeTestDescriptor {
 	protected String targetName;
 
@@ -82,20 +88,6 @@ public abstract class BaseRuntimeTestDescriptor implements RuntimeTestDescriptor
 		return null;
 	}
 
-	@Override
-	public String getAfterGrammar() {
-		try {
-			Field f = this.getClass().getField("afterGrammar");
-			String s = stringIndentation((String)f.get(this));
-			if ( s.length()==0 ) return null;
-			return s;
-		}
-		catch (Exception nsfe) {
-			; // we are optional
-		}
-		return null;
-	}
-
 	@Override
 	public Pair<String, String> getGrammar() {
 		String grammarName = null;

runtime-testsuite/test/org/antlr/v4/test/runtime/README.md

@@ -0,0 +1,5 @@
+# Runtime test mechanism
+
+The files in the various target subdirectories were automatically generated
+and exist as a convenience so that we can test individual targets and also
+groups of tests using the development environments like Intellij.

runtime-testsuite/test/org/antlr/v4/test/runtime/RuntimeTestDescriptor.java

@@ -4,23 +4,62 @@ import org.antlr.v4.runtime.misc.Pair;
 
 import java.util.List;
 
+/** This interface describes everything that a runtime test
+ *  descriptor can specify. Most testing descriptors will
+ *  subclass {@link BaseRuntimeTestDescriptor} rather than
+ *  implement this directly.  The {@link BaseRuntimeTest}
+ *  class pulls data from descriptors to execute tests.
+ *
+ *  @since 4.6
+ */
 public interface RuntimeTestDescriptor {
+	/** The name of this test such as TokenAndRuleContextString (see
+	 *  {@link org.antlr.v4.test.runtime.descriptors.ParseTreesDescriptors.TokenAndRuleContextString})
+	 */
 	String getTestName();
+
+	/** A type in {"Lexer", "Parser", "CompositeLexer", "CompositeParser"} */
 	String getTestType();
+
+	/** Parser input. Return "" if not input should be provided to the parser or lexer. */
 	String getInput();
+
+	/** Output from executing the parser. Return null if no output is expected. */
 	String getOutput();
+
+	/** Parse errors Return null if no errors are expected. */
 	String getErrors();
+
+	/** Errors generated by ANTLR processing the grammar. Return null if no errors are expected. */
 	String getANTLRToolErrors();
+
+	/** The rule at which parsing should start */
 	String getStartRule(); // TODO: alter tests to use same default start rule?
-	String getAfterGrammar(); // TODO: only a few use. make part of testrig or rename?
+
+	/** Initialization code */
+	//String getAfterGrammar(); // TODO: only a few use. make part of testrig or rename?
+
+	/** For lexical tests, dump the DFA of the default lexer mode to stdout */
 	boolean showDFA();
+
+	/** For parsing, engage the DiagnosticErrorListener, dumping results to stderr */
 	boolean showDiagnosticErrors();
 
-	Pair<String,String> getGrammar(); // Associates name of grammar like M in M.g4 to string (template) of grammar
+	/** Associates name of grammar like M in M.g4 to string (template) of grammar */
+	Pair<String,String> getGrammar();
+
+	/** Return a list of grammars imported into the grammar specified in {#getGrammar}. */
 	List<Pair<String,String>> getSlaveGrammars();
 
+	/** Return a string representing the name of the target currently testing
+	 *  this descriptor. Multiple instances of the same descriptor class
+	 *  can be created to test different targets.
+	 */
 	String getTarget();
+
+	/** Set the target we are testing */
 	void setTarget(String targetName);
 
+	/** Return true if this test should be ignored for the indicated target */
 	boolean ignore(String targetName);
 }

runtime-testsuite/test/org/antlr/v4/test/runtime/RuntimeTestSupport.java

@@ -1,6 +1,13 @@
 package org.antlr.v4.test.runtime;
 
-public interface SingleTest {
+/** This interface describes functionality needed to execute a runtime test.
+ *  Unfortunately the Base*Test.java files are big junk drawers. This is
+ *  an attempt to make it more obvious what new target implementers have to
+ *  implement.
+ *
+ *  @since 4.6
+ */
+public interface RuntimeTestSupport {
 	void testSetUp() throws Exception;
 	void testTearDown() throws Exception;
 	void eraseTempDir();

runtime-testsuite/test/org/antlr/v4/test/runtime/cpp/BaseCppTest.java

@@ -60,7 +60,7 @@ import org.antlr.v4.runtime.misc.Utils;
 import org.antlr.v4.runtime.tree.ParseTree;
 import org.antlr.v4.semantics.SemanticPipeline;
 import org.antlr.v4.test.runtime.ErrorQueue;
-import org.antlr.v4.test.runtime.SingleTest;
+import org.antlr.v4.test.runtime.RuntimeTestSupport;
 import org.antlr.v4.tool.ANTLRMessage;
 import org.antlr.v4.tool.DOTGenerator;
 import org.antlr.v4.tool.DefaultToolListener;
@@ -99,7 +99,7 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
-public class BaseCppTest implements SingleTest {
+public class BaseCppTest implements RuntimeTestSupport {
 	// -J-Dorg.antlr.v4.test.BaseTest.level=FINE
 	// private static final Logger LOGGER = Logger.getLogger(BaseTest.class.getName());
 	public static final String newline = System.getProperty("line.separator");

runtime-testsuite/test/org/antlr/v4/test/runtime/csharp/BaseCSharpTest.java

@@ -36,7 +36,7 @@ import org.antlr.v4.runtime.TokenSource;
 import org.antlr.v4.runtime.WritableToken;
 import org.antlr.v4.runtime.misc.Utils;
 import org.antlr.v4.test.runtime.ErrorQueue;
-import org.antlr.v4.test.runtime.SingleTest;
+import org.antlr.v4.test.runtime.RuntimeTestSupport;
 import org.antlr.v4.tool.ANTLRMessage;
 import org.antlr.v4.tool.DefaultToolListener;
 import org.antlr.v4.tool.GrammarSemanticsMessage;
@@ -77,7 +77,7 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
-public class BaseCSharpTest implements SingleTest {
+public class BaseCSharpTest implements RuntimeTestSupport {
 	public static final String newline = System.getProperty("line.separator");
 	public static final String pathSep = System.getProperty("path.separator");
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/CompositeLexersDescriptors.java

@@ -20,7 +20,7 @@ public class CompositeLexersDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "M";
 
@@ -60,7 +60,7 @@ public class CompositeLexersDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "M";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/CompositeParsersDescriptors.java

@@ -11,7 +11,7 @@ public class CompositeParsersDescriptors {
 	public static class BringInLiteralsFromDelegate extends BaseCompositeParserTestDescriptor {
 		public String input = "=a";
 		public String output = "S.a\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "M";
 
@@ -43,7 +43,7 @@ public class CompositeParsersDescriptors {
 	public static class CombinedImportsCombined extends BaseCompositeParserTestDescriptor {
 		public String input = "x 34 9";
 		public String output = "S.x\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "M";
 
@@ -92,7 +92,7 @@ public class CompositeParsersDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "M";
 
@@ -161,7 +161,7 @@ public class CompositeParsersDescriptors {
 	public static class DelegatorAccessesDelegateMembers extends BaseCompositeParserTestDescriptor {
 		public String input = "b";
 		public String output = "foo\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "M";
 
@@ -196,7 +196,7 @@ public class CompositeParsersDescriptors {
 	public static class DelegatorInvokesDelegateRule extends BaseCompositeParserTestDescriptor {
 		public String input = "b";
 		public String output = "S.a\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "M";
 
@@ -229,7 +229,7 @@ public class CompositeParsersDescriptors {
 	public static class DelegatorInvokesDelegateRuleWithArgs extends BaseCompositeParserTestDescriptor {
 		public String input = "b";
 		public String output = "S.a1000\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "M";
 
@@ -262,7 +262,7 @@ public class CompositeParsersDescriptors {
 	public static class DelegatorInvokesDelegateRuleWithReturnStruct extends BaseCompositeParserTestDescriptor {
 		public String input = "b";
 		public String output = "S.ab\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "M";
 
@@ -295,7 +295,7 @@ public class CompositeParsersDescriptors {
 	public static class DelegatorInvokesFirstVersionOfDelegateRule extends BaseCompositeParserTestDescriptor {
 		public String input = "b";
 		public String output = "S.a\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "M";
 
@@ -336,7 +336,7 @@ public class CompositeParsersDescriptors {
 	public static class DelegatorRuleOverridesDelegate extends BaseCompositeParserTestDescriptor {
 		public String input = "c";
 		public String output = "S.a\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "M";
 
@@ -375,7 +375,7 @@ public class CompositeParsersDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "M";
 
@@ -416,7 +416,7 @@ public class CompositeParsersDescriptors {
 	public static class DelegatorRuleOverridesLookaheadInDelegate extends BaseCompositeParserTestDescriptor {
 		public String input = "float x = 3;";
 		public String output = "JavaDecl: floatx=3;\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "prog";
 		public String grammarName = "M";
 
@@ -459,7 +459,7 @@ public class CompositeParsersDescriptors {
 	public static class ImportLexerWithOnlyFragmentRules extends BaseCompositeParserTestDescriptor {
 		public String input = "test test";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "program";
 		public String grammarName = "Test";
 
@@ -500,7 +500,7 @@ public class CompositeParsersDescriptors {
 	public static class ImportedGrammarWithEmptyOptions extends BaseCompositeParserTestDescriptor {
 		public String input = "b";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "M";
 
@@ -534,7 +534,7 @@ public class CompositeParsersDescriptors {
 	public static class ImportedRuleWithAction extends BaseCompositeParserTestDescriptor {
 		public String input = "b";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "M";
 
@@ -573,7 +573,7 @@ public class CompositeParsersDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "M";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/FullContextParsingDescriptors.java

@@ -205,7 +205,7 @@ public class FullContextParsingDescriptors {
 	}
 
 	public static abstract class FullContextIF_THEN_ELSEParse extends BaseDebugParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/LeftRecursionDescriptors.java

@@ -5,7 +5,7 @@ import org.antlr.v4.test.runtime.CommentHasStringValue;
 
 public class LeftRecursionDescriptors {
 	public static abstract class AmbigLR extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "prog";
 		public String grammarName = "Expr";
 
@@ -62,7 +62,7 @@ public class LeftRecursionDescriptors {
 	}
 
 	public static abstract class Declarations extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -90,7 +90,7 @@ public class LeftRecursionDescriptors {
 	public static class Declarations_1 extends Declarations {
 		public String input = "a";
 		public String output = "(s (declarator a) <EOF>)\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -166,7 +166,7 @@ public class LeftRecursionDescriptors {
 	 * https://github.com/antlr/antlr4/issues/161
 	 */
 	public static abstract class DirectCallToLeftRecursiveRule extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -199,7 +199,7 @@ public class LeftRecursionDescriptors {
 	}
 
 	public static abstract class Expressions extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -259,7 +259,7 @@ public class LeftRecursionDescriptors {
 	}
 
 	public static abstract class JavaExpressions extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -388,7 +388,7 @@ public class LeftRecursionDescriptors {
 	}
 
 	public static abstract class LabelsOnOpSubrule extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -428,7 +428,7 @@ public class LeftRecursionDescriptors {
 	 * https://github.com/antlr/antlr4/issues/625
 	 */
 	public static abstract class MultipleActionsPredicatesOptions extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -469,7 +469,7 @@ public class LeftRecursionDescriptors {
 	 * https://github.com/antlr/antlr4/issues/625
 	 */
 	public static abstract class MultipleActions extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -491,7 +491,7 @@ public class LeftRecursionDescriptors {
 	public static class MultipleActions_1 extends MultipleActions {
 		public String input = "4";
 		public String output = "(s (e 4))\n";
-		public String errors = "";
+		public String errors = null;
 	}
 
 	public static class MultipleActions_2 extends MultipleActions {
@@ -513,7 +513,7 @@ public class LeftRecursionDescriptors {
 	public static abstract class MultipleAlternativesWithCommonLabel extends BaseParserTestDescriptor {
 		public String startRule = "s";
 		public String grammarName = "T";
-		public String errors = "";
+		public String errors = null;
 
 		/**
 		 grammar T;
@@ -566,7 +566,7 @@ public class LeftRecursionDescriptors {
 	public static class PrecedenceFilterConsidersContext extends BaseParserTestDescriptor {
 		public String input = "aa";
 		public String output = "(prog (statement (letterA a)) (statement (letterA a)) <EOF>)\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "prog";
 		public String grammarName = "T";
 
@@ -584,7 +584,7 @@ public class LeftRecursionDescriptors {
 	}
 
 	public static abstract class PrefixAndOtherAlt extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -616,7 +616,7 @@ public class LeftRecursionDescriptors {
 	}
 
 	public static abstract class PrefixOpWithActionAndLabel extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -653,7 +653,7 @@ public class LeftRecursionDescriptors {
 	}
 
 	public static abstract class ReturnValueAndActionsAndLabels extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -707,7 +707,7 @@ public class LeftRecursionDescriptors {
 	 * to a ternary operator).
 	 */
 	public static abstract class ReturnValueAndActionsList extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -759,7 +759,7 @@ public class LeftRecursionDescriptors {
 	 * This test treats the `,` and `>>` operators separately.
 	 */
 	public static abstract class ReturnValueAndActionsList2 extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -803,7 +803,7 @@ public class LeftRecursionDescriptors {
 	}
 
 	public static abstract class ReturnValueAndActions extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -848,7 +848,7 @@ public class LeftRecursionDescriptors {
 	public static class SemPred extends BaseParserTestDescriptor {
 		public String input = "x y z";
 		public String output = "(s (a (a (a x) y) z))\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -888,7 +888,7 @@ public class LeftRecursionDescriptors {
 	}
 
 	public static abstract class Simple extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -927,7 +927,7 @@ public class LeftRecursionDescriptors {
 	 * https://github.com/antlr/antlr4/issues/542
 	 */
 	public static abstract class TernaryExprExplicitAssociativity extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -994,7 +994,7 @@ public class LeftRecursionDescriptors {
 	}
 
 	public static abstract class TernaryExpr extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -1068,7 +1068,7 @@ public class LeftRecursionDescriptors {
 	public static abstract class WhitespaceInfluence extends BaseParserTestDescriptor {
 		public String input = "Test(1,3)";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "prog";
 		public String grammarName = "Expr";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/LexerErrorsDescriptors.java

@@ -54,7 +54,7 @@ public class LexerErrorsDescriptors {
 	}
 
 	public static abstract class EnforcedGreedyNestedBraces extends BaseLexerTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -212,7 +212,7 @@ public class LexerErrorsDescriptors {
 	}
 
 	public static abstract class StringsEmbeddedInActions extends BaseLexerTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/LexerExecDescriptors.java

@@ -22,7 +22,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -53,7 +53,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -79,7 +79,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -103,7 +103,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -129,7 +129,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -159,7 +159,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -186,7 +186,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -210,7 +210,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -234,7 +234,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -258,7 +258,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -282,7 +282,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -306,7 +306,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -329,7 +329,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -344,7 +344,7 @@ public class LexerExecDescriptors {
 	}
 
 	public static abstract class EOFSuffixInFirstRule extends BaseLexerTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -389,7 +389,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -413,7 +413,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -443,7 +443,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -472,7 +472,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -507,7 +507,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -541,7 +541,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -572,7 +572,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -598,7 +598,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -629,7 +629,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -659,7 +659,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -683,7 +683,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -705,7 +705,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -733,7 +733,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -778,7 +778,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "PositionAdjustingLexer";
 
@@ -832,7 +832,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -846,7 +846,7 @@ public class LexerExecDescriptors {
 	}
 
 	public static abstract class RecursiveLexerRuleRefWithWildcardPlus extends BaseLexerTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -896,7 +896,7 @@ public class LexerExecDescriptors {
 	}
 
 	public static abstract class RecursiveLexerRuleRefWithWildcardStar extends BaseLexerTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -958,7 +958,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -985,7 +985,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -1018,7 +1018,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -1051,7 +1051,7 @@ public class LexerExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/ListenersDescriptors.java

@@ -14,7 +14,7 @@ public class ListenersDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -57,7 +57,7 @@ public class ListenersDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -100,7 +100,7 @@ public class ListenersDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -132,7 +132,7 @@ public class ListenersDescriptors {
 	}
 
 	public static abstract class RuleGetters extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -184,7 +184,7 @@ public class ListenersDescriptors {
 	}
 
 	public static abstract class TokenGetters extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/ParseTreesDescriptors.java

@@ -7,7 +7,7 @@ public class ParseTreesDescriptors {
 	public static class AltNum extends BaseParserTestDescriptor {
 		public String input = "xyz";
 		public String output = "(a:3 x (b:2 y) z)\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -99,7 +99,7 @@ public class ParseTreesDescriptors {
 	public static class RuleRef extends BaseParserTestDescriptor {
 		public String input = "yx";
 		public String output = "(a (b y) x)\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -153,7 +153,7 @@ public class ParseTreesDescriptors {
 	public static class Token2 extends BaseParserTestDescriptor {
 		public String input = "xy";
 		public String output = "(a x y)\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -184,7 +184,7 @@ public class ParseTreesDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -210,7 +210,7 @@ public class ParseTreesDescriptors {
 	public static class TwoAltLoop extends BaseParserTestDescriptor {
 		public String input = "xyyxyxz";
 		public String output = "(a x y y x y x z)\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -235,7 +235,7 @@ public class ParseTreesDescriptors {
 	public static class TwoAlts extends BaseParserTestDescriptor {
 		public String input = "y";
 		public String output = "(a y)\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/ParserErrorsDescriptors.java

@@ -43,7 +43,7 @@ public class ParserErrorsDescriptors {
 	public static class ContextListGetters extends BaseParserTestDescriptor {
 		public String input = "abab";
 		public String output = "abab\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -63,7 +63,7 @@ public class ParserErrorsDescriptors {
 
 	public static abstract class DuplicatedLeftRecursiveCall extends BaseParserTestDescriptor {
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "start";
 		public String grammarName = "T";
 
@@ -106,7 +106,7 @@ public class ParserErrorsDescriptors {
 	public static class InvalidATNStateRemoval extends BaseParserTestDescriptor {
 		public String input = "x:x";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "start";
 		public String grammarName = "T";
 
@@ -146,7 +146,7 @@ public class ParserErrorsDescriptors {
 	public static class LL1ErrorInfo extends BaseParserTestDescriptor {
 		public String input = "dog and software";
 		public String output = "{'hardware', 'software'}\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "start";
 		public String grammarName = "T";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/ParserExecDescriptors.java

@@ -7,7 +7,7 @@ public class ParserExecDescriptors {
 	public static class APlus extends BaseParserTestDescriptor {
 		public String input = "a b c";
 		public String output = "abc\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -27,7 +27,7 @@ public class ParserExecDescriptors {
 	public static class AStar_1 extends BaseParserTestDescriptor {
 		public String input = "";
 		public String output = "\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -47,7 +47,7 @@ public class ParserExecDescriptors {
 	public static class AStar_2 extends BaseParserTestDescriptor {
 		public String input = "a b c";
 		public String output = "abc\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -67,7 +67,7 @@ public class ParserExecDescriptors {
 	public static class AorAPlus extends BaseParserTestDescriptor {
 		public String input = "a b c";
 		public String output = "abc\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -87,7 +87,7 @@ public class ParserExecDescriptors {
 	public static class AorAStar_1 extends BaseParserTestDescriptor {
 		public String input = "";
 		public String output = "\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -107,7 +107,7 @@ public class ParserExecDescriptors {
 	public static class AorAStar_2 extends BaseParserTestDescriptor {
 		public String input = "a b c";
 		public String output = "abc\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -127,7 +127,7 @@ public class ParserExecDescriptors {
 	public static class AorB extends BaseParserTestDescriptor {
 		public String input = "34";
 		public String output = "alt 2\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -150,7 +150,7 @@ public class ParserExecDescriptors {
 	public static class AorBPlus extends BaseParserTestDescriptor {
 		public String input = "a 34 c";
 		public String output = "a34c\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -172,7 +172,7 @@ public class ParserExecDescriptors {
 	public static class AorBStar_1 extends BaseParserTestDescriptor {
 		public String input = "";
 		public String output = "\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -194,7 +194,7 @@ public class ParserExecDescriptors {
 	public static class AorBStar_2 extends BaseParserTestDescriptor {
 		public String input = "a 34 c";
 		public String output = "a34c\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -216,7 +216,7 @@ public class ParserExecDescriptors {
 	public static class Basic extends BaseParserTestDescriptor {
 		public String input = "abc 34";
 		public String output = "abc34\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -242,7 +242,7 @@ public class ParserExecDescriptors {
 	public static class EOFInClosure extends BaseParserTestDescriptor {
 		public String input = "x";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "prog";
 		public String grammarName = "T";
 
@@ -265,7 +265,7 @@ public class ParserExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "start";
 		public String grammarName = "T";
 
@@ -293,7 +293,7 @@ public class ParserExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "start";
 		public String grammarName = "T";
 
@@ -321,7 +321,7 @@ public class ParserExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "start";
 		public String grammarName = "T";
 
@@ -349,7 +349,7 @@ public class ParserExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "start";
 		public String grammarName = "T";
 
@@ -371,7 +371,7 @@ public class ParserExecDescriptors {
 	public static class LL1OptionalBlock_1 extends BaseParserTestDescriptor {
 		public String input = "";
 		public String output = "\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -392,7 +392,7 @@ public class ParserExecDescriptors {
 	public static class LL1OptionalBlock_2 extends BaseParserTestDescriptor {
 		public String input = "a";
 		public String output = "a\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -424,7 +424,7 @@ public class ParserExecDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "start";
 		public String grammarName = "T";
 
@@ -446,7 +446,7 @@ public class ParserExecDescriptors {
 	public static class Labels extends BaseParserTestDescriptor {
 		public String input = "abc 34;";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -471,7 +471,7 @@ public class ParserExecDescriptors {
 	public static class ListLabelForClosureContext extends BaseParserTestDescriptor {
 		public String input = "a";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "expression";
 		public String grammarName = "T";
 
@@ -510,7 +510,7 @@ public class ParserExecDescriptors {
 	public static class ListLabelsOnSet extends BaseParserTestDescriptor {
 		public String input = "abc 34;";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -536,7 +536,7 @@ public class ParserExecDescriptors {
 	public static class MultipleEOFHandling extends BaseParserTestDescriptor {
 		public String input = "x";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "prog";
 		public String grammarName = "T";
 
@@ -556,7 +556,7 @@ public class ParserExecDescriptors {
 	public static class Optional_1 extends BaseParserTestDescriptor {
 		public String input = "x";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "stat";
 		public String grammarName = "T";
 
@@ -574,7 +574,7 @@ public class ParserExecDescriptors {
 	public static class Optional_2 extends BaseParserTestDescriptor {
 		public String input = "if x";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "stat";
 		public String grammarName = "T";
 
@@ -592,7 +592,7 @@ public class ParserExecDescriptors {
 	public static class Optional_3 extends BaseParserTestDescriptor {
 		public String input = "if x else x";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "stat";
 		public String grammarName = "T";
 
@@ -610,7 +610,7 @@ public class ParserExecDescriptors {
 	public static class Optional_4 extends BaseParserTestDescriptor {
 		public String input = "if if x else x";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "stat";
 		public String grammarName = "T";
 
@@ -633,7 +633,7 @@ public class ParserExecDescriptors {
 	public static class ParserProperty extends BaseParserTestDescriptor {
 		public String input = "abc";
 		public String output = "valid\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -657,7 +657,7 @@ public class ParserExecDescriptors {
 	public static class PredicatedIfIfElse extends BaseParserTestDescriptor {
 		public String input = "if x if x a else b";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -683,7 +683,7 @@ public class ParserExecDescriptors {
 	public static class PredictionIssue334 extends BaseParserTestDescriptor {
 		public String input = "a";
 		public String output = "(file_ (item a) <EOF>)\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "file_";
 		public String grammarName = "T";
 
@@ -715,7 +715,7 @@ public class ParserExecDescriptors {
 	public static class ReferenceToATN_1 extends BaseParserTestDescriptor {
 		public String input = "";
 		public String output = "\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -734,7 +734,7 @@ public class ParserExecDescriptors {
 	public static class ReferenceToATN_2 extends BaseParserTestDescriptor {
 		public String input = "a 34 c";
 		public String output = "a34c\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/PerformanceDescriptors.java

@@ -11,7 +11,7 @@ public class PerformanceDescriptors {
 	 */
 	public static abstract class ExpressionGrammar extends BaseParserTestDescriptor {
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "program";
 		public String grammarName = "Expr";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/SemPredEvalLexerDescriptors.java

@@ -21,7 +21,7 @@ public class SemPredEvalLexerDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -52,7 +52,7 @@ public class SemPredEvalLexerDescriptors {
 
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -82,7 +82,7 @@ public class SemPredEvalLexerDescriptors {
 
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -118,7 +118,7 @@ public class SemPredEvalLexerDescriptors {
 		@CommentHasStringValue // 	no 'm'-> transition...conflicts with pred
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -158,7 +158,7 @@ public class SemPredEvalLexerDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -193,7 +193,7 @@ public class SemPredEvalLexerDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 
@@ -226,7 +226,7 @@ public class SemPredEvalLexerDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "";
 		public String grammarName = "L";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/SemPredEvalParserDescriptors.java

@@ -14,7 +14,7 @@ public class SemPredEvalParserDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -48,7 +48,7 @@ public class SemPredEvalParserDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -77,7 +77,7 @@ public class SemPredEvalParserDescriptors {
 	public static class AtomWithClosureInTranslatedLRRule extends BaseParserTestDescriptor {
 		public String input = "a+b+a";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "start";
 		public String grammarName = "T";
 
@@ -106,7 +106,7 @@ public class SemPredEvalParserDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -131,7 +131,7 @@ public class SemPredEvalParserDescriptors {
 	public static class DependentPredNotInOuterCtxShouldBeIgnored extends BaseParserTestDescriptor {
 		public String input = "a;";
 		public String output = "alt 2\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -160,7 +160,7 @@ public class SemPredEvalParserDescriptors {
 	public static class DisabledAlternative extends BaseParserTestDescriptor {
 		public String input = "hello";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "cppCompilationUnit";
 		public String grammarName = "T";
 
@@ -179,7 +179,7 @@ public class SemPredEvalParserDescriptors {
 	public static class IndependentPredNotPassedOuterCtxToAvoidCastException extends BaseParserTestDescriptor {
 		public String input = "a;";
 		public String output = "alt 2\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -231,7 +231,7 @@ public class SemPredEvalParserDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -287,11 +287,11 @@ public class SemPredEvalParserDescriptors {
 	public static class PredFromAltTestedInLoopBack_2 extends PredFromAltTestedInLoopBack {
 		public String input = "s\n\n\nx\n\n";
 		public String output = "(file_ (para (paraContent s) \\n \\n) (para (paraContent \\n x) \\n \\n) <EOF>)\n";
-		public String errors = "";
+		public String errors = null;
 	}
 
 	public static abstract class PredTestedEvenWhenUnAmbig extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "primary";
 		public String grammarName = "T";
 
@@ -336,7 +336,7 @@ public class SemPredEvalParserDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -370,7 +370,7 @@ public class SemPredEvalParserDescriptors {
 	public static class PredicateDependentOnArg2 extends BaseParserTestDescriptor {
 		public String input = "a b";
 		public String output = "";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -403,7 +403,7 @@ public class SemPredEvalParserDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -433,7 +433,7 @@ public class SemPredEvalParserDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -462,7 +462,7 @@ public class SemPredEvalParserDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -542,7 +542,7 @@ public class SemPredEvalParserDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -579,7 +579,7 @@ public class SemPredEvalParserDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -684,7 +684,7 @@ public class SemPredEvalParserDescriptors {
 	public static class UnpredicatedPathsInAlt extends BaseParserTestDescriptor {
 		public String input = "x 4";
 		public String output = "alt 1\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/SetsDescriptors.java

@@ -15,7 +15,7 @@ public class SetsDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -56,7 +56,7 @@ public class SetsDescriptors {
 	public static class LexerOptionalSet extends BaseParserTestDescriptor {
 		public String input = "ac";
 		public String output = "ac\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -73,7 +73,7 @@ public class SetsDescriptors {
 	public static class LexerPlusSet extends BaseParserTestDescriptor {
 		public String input = "abaac";
 		public String output = "abaac\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -90,7 +90,7 @@ public class SetsDescriptors {
 	public static class LexerStarSet extends BaseParserTestDescriptor {
 		public String input = "abaac";
 		public String output = "abaac\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -107,7 +107,7 @@ public class SetsDescriptors {
 	public static class NotChar extends BaseParserTestDescriptor {
 		public String input = "x";
 		public String output = "x\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -124,7 +124,7 @@ public class SetsDescriptors {
 	public static class NotCharSet extends BaseParserTestDescriptor {
 		public String input = "x";
 		public String output = "x\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -141,7 +141,7 @@ public class SetsDescriptors {
 	public static class NotCharSetWithLabel extends BaseParserTestDescriptor {
 		public String input = "x";
 		public String output = "x\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -158,7 +158,7 @@ public class SetsDescriptors {
 	public static class NotCharSetWithRuleRef3 extends BaseParserTestDescriptor {
 		public String input = "x";
 		public String output = "x\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -177,7 +177,7 @@ public class SetsDescriptors {
 	public static class OptionalLexerSingleElement extends BaseParserTestDescriptor {
 		public String input = "bc";
 		public String output = "bc\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -194,7 +194,7 @@ public class SetsDescriptors {
 	public static class OptionalSet extends BaseParserTestDescriptor {
 		public String input = "ac";
 		public String output = "ac\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -210,7 +210,7 @@ public class SetsDescriptors {
 	public static class OptionalSingleElement extends BaseParserTestDescriptor {
 		public String input = "bc";
 		public String output = "bc\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -227,7 +227,7 @@ public class SetsDescriptors {
 	public static class ParserNotSet extends BaseParserTestDescriptor {
 		public String input = "zz";
 		public String output = "z\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -243,7 +243,7 @@ public class SetsDescriptors {
 	public static class ParserNotToken extends BaseParserTestDescriptor {
 		public String input = "zz";
 		public String output = "zz\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -259,7 +259,7 @@ public class SetsDescriptors {
 	public static class ParserNotTokenWithLabel extends BaseParserTestDescriptor {
 		public String input = "zz";
 		public String output = "z\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -275,7 +275,7 @@ public class SetsDescriptors {
 	public static class ParserSet extends BaseParserTestDescriptor {
 		public String input = "x";
 		public String output = "x\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -291,7 +291,7 @@ public class SetsDescriptors {
 	public static class PlusLexerSingleElement extends BaseParserTestDescriptor {
 		public String input = "bbbbc";
 		public String output = "bbbbc\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -308,7 +308,7 @@ public class SetsDescriptors {
 	public static class PlusSet extends BaseParserTestDescriptor {
 		public String input = "abaac";
 		public String output = "abaac\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -324,7 +324,7 @@ public class SetsDescriptors {
 	public static class RuleAsSet extends BaseParserTestDescriptor {
 		public String input = "b";
 		public String output = "b\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -340,7 +340,7 @@ public class SetsDescriptors {
 	public static class SeqDoesNotBecomeSet extends BaseParserTestDescriptor {
 		public String input = "34";
 		public String output = "34\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -357,7 +357,7 @@ public class SetsDescriptors {
 	}
 
 	public static abstract class StarLexerSingleElement extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 
@@ -384,7 +384,7 @@ public class SetsDescriptors {
 	public static class StarSet extends BaseParserTestDescriptor {
 		public String input = "abaac";
 		public String output = "abaac\n";
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "a";
 		public String grammarName = "T";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/VisitorsDescriptors.java

@@ -22,7 +22,7 @@ public class VisitorsDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -67,7 +67,7 @@ public class VisitorsDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -113,7 +113,7 @@ public class VisitorsDescriptors {
 		@CommentHasStringValue
 		public String output;
 
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -151,7 +151,7 @@ public class VisitorsDescriptors {
 	}
 
 	public static abstract class RuleGetters extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 
@@ -209,7 +209,7 @@ public class VisitorsDescriptors {
 	}
 
 	public static abstract class TokenGetters extends BaseParserTestDescriptor {
-		public String errors = "";
+		public String errors = null;
 		public String startRule = "s";
 		public String grammarName = "T";
 

runtime-testsuite/test/org/antlr/v4/test/runtime/go/BaseGoTest.java

@@ -57,7 +57,7 @@ import org.antlr.v4.runtime.misc.Interval;
 import org.antlr.v4.runtime.misc.Utils;
 import org.antlr.v4.semantics.SemanticPipeline;
 import org.antlr.v4.test.runtime.ErrorQueue;
-import org.antlr.v4.test.runtime.SingleTest;
+import org.antlr.v4.test.runtime.RuntimeTestSupport;
 import org.antlr.v4.tool.ANTLRMessage;
 import org.antlr.v4.tool.DOTGenerator;
 import org.antlr.v4.tool.DefaultToolListener;
@@ -97,7 +97,7 @@ import static junit.framework.TestCase.assertNotNull;
 import static junit.framework.TestCase.assertTrue;
 import static org.junit.Assert.assertArrayEquals;
 
-public class BaseGoTest implements SingleTest {
+public class BaseGoTest implements RuntimeTestSupport {
 	// -J-Dorg.antlr.v4.test.BaseTest.level=FINE
 	// private static final Logger LOGGER =
 	// Logger.getLogger(BaseTest.class.getName());

runtime-testsuite/test/org/antlr/v4/test/runtime/java/BaseJavaTest.java

@@ -61,7 +61,7 @@ import org.antlr.v4.runtime.misc.Utils;
 import org.antlr.v4.runtime.tree.ParseTree;
 import org.antlr.v4.semantics.SemanticPipeline;
 import org.antlr.v4.test.runtime.ErrorQueue;
-import org.antlr.v4.test.runtime.SingleTest;
+import org.antlr.v4.test.runtime.RuntimeTestSupport;
 import org.antlr.v4.tool.ANTLRMessage;
 import org.antlr.v4.tool.DefaultToolListener;
 import org.antlr.v4.tool.Grammar;
@@ -109,7 +109,7 @@ import static junit.framework.TestCase.assertNotNull;
 import static junit.framework.TestCase.assertTrue;
 import static org.junit.Assert.assertArrayEquals;
 
-public class BaseJavaTest implements SingleTest {
+public class BaseJavaTest implements RuntimeTestSupport {
 	// -J-Dorg.antlr.v4.test.BaseTest.level=FINE
 	private static final Logger LOGGER = Logger.getLogger(BaseJavaTest.class.getName());
 

runtime-testsuite/test/org/antlr/v4/test/runtime/javascript/browser/BaseBrowserTest.java

@@ -57,7 +57,7 @@ import org.antlr.v4.runtime.misc.Interval;
 import org.antlr.v4.runtime.misc.Utils;
 import org.antlr.v4.semantics.SemanticPipeline;
 import org.antlr.v4.test.runtime.ErrorQueue;
-import org.antlr.v4.test.runtime.SingleTest;
+import org.antlr.v4.test.runtime.RuntimeTestSupport;
 import org.antlr.v4.tool.ANTLRMessage;
 import org.antlr.v4.tool.DOTGenerator;
 import org.antlr.v4.tool.DefaultToolListener;
@@ -103,7 +103,7 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
-public abstract class BaseBrowserTest implements SingleTest {
+public abstract class BaseBrowserTest implements RuntimeTestSupport {
 	// -J-Dorg.antlr.v4.test.BaseTest.level=FINE
 	// private static final Logger LOGGER = Logger.getLogger(BaseTest.class.getName());
 

runtime-testsuite/test/org/antlr/v4/test/runtime/javascript/node/BaseNodeTest.java

@@ -57,7 +57,7 @@ import org.antlr.v4.runtime.misc.Interval;
 import org.antlr.v4.runtime.misc.Utils;
 import org.antlr.v4.semantics.SemanticPipeline;
 import org.antlr.v4.test.runtime.ErrorQueue;
-import org.antlr.v4.test.runtime.SingleTest;
+import org.antlr.v4.test.runtime.RuntimeTestSupport;
 import org.antlr.v4.tool.ANTLRMessage;
 import org.antlr.v4.tool.DOTGenerator;
 import org.antlr.v4.tool.DefaultToolListener;
@@ -95,7 +95,7 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
-public class BaseNodeTest implements SingleTest {
+public class BaseNodeTest implements RuntimeTestSupport {
 	// -J-Dorg.antlr.v4.test.BaseTest.level=FINE
 	// private static final Logger LOGGER =
 	// Logger.getLogger(BaseTest.class.getName());

runtime-testsuite/test/org/antlr/v4/test/runtime/python/BasePythonTest.java

@@ -60,7 +60,7 @@ import org.antlr.v4.runtime.misc.Utils;
 import org.antlr.v4.runtime.tree.ParseTree;
 import org.antlr.v4.semantics.SemanticPipeline;
 import org.antlr.v4.test.runtime.ErrorQueue;
-import org.antlr.v4.test.runtime.SingleTest;
+import org.antlr.v4.test.runtime.RuntimeTestSupport;
 import org.antlr.v4.tool.ANTLRMessage;
 import org.antlr.v4.tool.DOTGenerator;
 import org.antlr.v4.tool.DefaultToolListener;
@@ -101,7 +101,7 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
-public abstract class BasePythonTest implements SingleTest {
+public abstract class BasePythonTest implements RuntimeTestSupport {
 	// -J-Dorg.antlr.v4.test.BaseTest.level=FINE
 	// private static final Logger LOGGER = Logger.getLogger(BaseTest.class.getName());
 	public static final String newline = System.getProperty("line.separator");