Using ini-file option instead of cmd option.

src/_pytest/assertion/__init__.py

@@ -23,11 +23,10 @@ def pytest_addoption(parser):
                             test modules on import to provide assert
                             expression information.""",
     )
-
-    group = parser.getgroup("experimental")
-    group.addoption(
-        "--enable-assertion-pass-hook",
-        action="store_true",
+    parser.addini(
+        "enable_assertion_pass_hook",
+        type="bool",
+        default="False",
         help="Enables the pytest_assertion_pass hook."
         "Make sure to delete any previously generated pyc cache files.",
     )

src/_pytest/assertion/rewrite.py

@@ -604,6 +604,10 @@ class AssertionRewriter(ast.NodeVisitor):
         super().__init__()
         self.module_path = module_path
         self.config = config
+        if config is not None:
+            self.enable_assertion_pass_hook = config.getini("enable_assertion_pass_hook")
+        else:
+            self.enable_assertion_pass_hook = False
 
     def run(self, mod):
         """Find all assert statements in *mod* and rewrite them."""
@@ -745,7 +749,7 @@ class AssertionRewriter(ast.NodeVisitor):
         format_dict = ast.Dict(keys, list(current.values()))
         form = ast.BinOp(expl_expr, ast.Mod(), format_dict)
         name = "@py_format" + str(next(self.variable_counter))
-        if getattr(self.config._ns, "enable_assertion_pass_hook", False):
+        if self.enable_assertion_pass_hook:
             self.format_variables.append(name)
         self.expl_stmts.append(ast.Assign([ast.Name(name, ast.Store())], form))
         return ast.Name(name, ast.Load())
@@ -782,7 +786,7 @@ class AssertionRewriter(ast.NodeVisitor):
         self.variables = []
         self.variable_counter = itertools.count()
 
-        if getattr(self.config._ns, "enable_assertion_pass_hook", False):
+        if self.enable_assertion_pass_hook:
             self.format_variables = []
 
         self.stack = []
@@ -797,7 +801,7 @@ class AssertionRewriter(ast.NodeVisitor):
                     top_condition, module_path=self.module_path, lineno=assert_.lineno
                 )
             )
-        if getattr(self.config._ns, "enable_assertion_pass_hook", False):
+        if self.enable_assertion_pass_hook:
             ### Experimental pytest_assertion_pass hook
             negation = ast.UnaryOp(ast.Not(), top_condition)
             msg = self.pop_format_context(ast.Str(explanation))

src/_pytest/hookspec.py

@@ -503,7 +503,7 @@ def pytest_assertion_pass(item, lineno, orig, expl):
     This hook is still *experimental*, so its parameters or even the hook itself might
     be changed/removed without warning in any future pytest release.
 
-    It should be enabled using the `--enable-assertion-pass-hook` command line option.
+    It should be enabled using the `enable_assertion_pass_hook` ini-file option.
     Remember to clean the .pyc files in your project directory and interpreter libraries.
 
     If you find this hook useful, please share your feedback opening an issue.

testing/test_assertrewrite.py

@@ -1308,6 +1308,7 @@ class TestEarlyRewriteBailout:
 
 
 class TestAssertionPass:
+
     def test_hook_call(self, testdir):
         testdir.makeconftest(
             """
@@ -1315,6 +1316,12 @@ class TestAssertionPass:
                 raise Exception("Assertion Passed: {} {} at line {}".format(orig, expl, lineno))
             """
         )
+
+        testdir.makeini("""
+        [pytest]
+        enable_assertion_pass_hook = True
+        """)
+
         testdir.makepyfile(
             """
             def test_simple():
@@ -1326,7 +1333,7 @@ class TestAssertionPass:
                 assert a+b == c+d
             """
         )
-        result = testdir.runpytest("--enable-assertion-pass-hook")
+        result = testdir.runpytest()
         result.stdout.fnmatch_lines(
             "*Assertion Passed: a + b == c + d (1 + 2) == (3 + 0) at line 7*"
         )
@@ -1342,6 +1349,11 @@ class TestAssertionPass:
             _pytest.assertion.rewrite, "_call_assertion_pass", raise_on_assertionpass
         )
 
+        testdir.makeini("""
+        [pytest]
+        enable_assertion_pass_hook = True
+        """)
+
         testdir.makepyfile(
             """
             def test_simple():
@@ -1353,7 +1365,7 @@ class TestAssertionPass:
                 assert a+b == c+d
             """
         )
-        result = testdir.runpytest("--enable-assertion-pass-hook")
+        result = testdir.runpytest()
         result.assert_outcomes(passed=1)
 
     def test_hook_not_called_without_cmd_option(self, testdir, monkeypatch):
@@ -1374,6 +1386,11 @@ class TestAssertionPass:
             """
         )
 
+        testdir.makeini("""
+        [pytest]
+        enable_assertion_pass_hook = False
+        """)
+
         testdir.makepyfile(
             """
             def test_simple():