Because ANTLR supports multiple target languages, the unit tests are broken into two groups: the unit tests that test the tool itself (in `tool-testsuite`) and the unit tests that test the parser runtimes (in `antlr4/runtime-testsuite`). The tool tests are straightforward because they are Java code testing Java code; see the section at the bottom of this file.
The runtime tests must be specified in a generic fashion to work across language targets. Furthermore, we must test the various targets from Java. This usually means Java launching processes to compile, say, C++ and run parsers.
As of 4.6, we use [a Java descriptor object](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/RuntimeTestDescriptor.java) to describe each runtime test. Unit tests are grouped together into categories such as [ParserExecDescriptors](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/ParserExecDescriptors.java), which has multiple nested descriptor objects, one per test. For example, here is the start of that file:
```java
public class ParserExecDescriptors {
public static class APlus extends BaseParserTestDescriptor {
The mysterious `@CommentHasStringValue` annotation is a bit of a hack that allows multi-line strings in Java. This kung fu is required so that we can use Java classes rather than StringTemplate group files to specify runtime tests (the legacy system used those and it was hard to get them right). Here are all the [Runtime test descriptors](https://github.com/antlr/antlr4/tree/master/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors) organized into groups.
The grammars are strings representing StringTemplates (`ST` objects) so `<writeln("$text")>` will get replace when the unit test file is generated (`Test.java`, `Test.cs`, ...). The `writeln` template must be defined per target. Here are all of the
[Target templates for runtime tests](https://github.com/antlr/antlr4/tree/master/runtime-testsuite/resources/org/antlr/v4/test/runtime/templates).
*`mono` (e.g., `brew install mono`) on non-Windows boxes (on Windows it uses the Microsoft .net stack). Also must [`xbuild` the runtime](https://github.com/antlr/antlr4/blob/master/doc/releasing-antlr.md) before tests will run; see below
A single test rig is sufficient to test all targets against all descriptors using the [junit parameterized tests](https://github.com/junit-team/junit4/wiki/parameterized-tests) mechanism. But, that is inconvenient because we often want to test just a single target or perhaps even just a single test within a single group of a single target. I have automatically generated a bunch of
[Target runtime test rigs](https://github.com/antlr/antlr4/tree/master/runtime-testsuite/test/org/antlr/v4/test/runtime) that allow developers such flexibility. For example, here are the Python3 test rigs in intellij:
To add a new runtime test, first determine which [group of tests](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors) it belongs to. Then, add a new [RuntimeTestDescriptor](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/RuntimeTestDescriptor.java) implementation by subclassing one of:
* [BaseParserTestDescriptor](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/BaseParserTestDescriptor.java); see example [APlus](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/ParserExecDescriptors.java#L7).
* [BaseDiagnosticParserTestDescriptor](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/BaseDiagnosticParserTestDescriptor) if you want to test parser diagnostic output; see [example output](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/FullContextParsingDescriptors.java#L16).
* [BaseCompositeParserTestDescriptor](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/BaseCompositeParserTestDescriptor.java); see example [BringInLiteralsFromDelegate](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/CompositeParsersDescriptors.java#L11)
* [BaseLexerTestDescriptor](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/BaseLexerTestDescriptor.java); see example [ActionPlacement](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/LexerExecDescriptors.java#L12).
* [BaseCompositeLexerTestDescriptor](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/BaseCompositeLexerTestDescriptor.java); see example [LexerDelegatorInvokesDelegateRule](https://github.com/antlr/antlr4/blob/master/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/CompositeLexersDescriptors.java#L11)
Your best bet is to find a similar test in the appropriate group and then copy and paste the descriptor object, creating a new nested class within the test group class. Modify the field definitions to suit your new problem.
If you need to create a whole new group of tests, it requires a new descriptor class; call it `XDescriptors`. Then, in each [target subdirectory](https://github.com/antlr/antlr4/tree/master/runtime-testsuite/test/org/antlr/v4/test/runtime), you need to create a new test rig `TestX.java` file:
where `<TARGET>` is replaced with Java, Cpp, CSharp, Python2, ... in the various subdirectories.
### Ignoring tests
In order to turn off a test for a particular target, we need to use the `ignore` method. Given a target name, a descriptor object can decide whether to ignore the test. This is not always convenient but it is fully general and works well for the one case we have now where we have to ignore `Visitor` tests in all targets except JavaScript.
Some parts of the runtime API need to be tested with code written specifically in the target language. For example, you can see all of the Java runtime API tests here:
Just go into the appropriate Java test class in dir [antlr4/tool-testsuite/test/org/antlr/v4/test/tool](https://github.com/antlr/antlr4/tree/master/tool-testsuite/test/org/antlr/v4/test/tool) and add your unit test.
