Fix parameter handling of non-static test methods

by supporting positional-only self parameters in
_pytest.compat.getfuncargnames()

Fixes #13376

Co-authored-by: Bruno Oliveira <[email protected]>

Author: purplezimmermann

Diff for: changelog/13377.bugfix.rst

@@ -0,0 +1,28 @@
+Fixed handling of test methods with special parameter syntax.
+
+Now, methods are supported that formally define ``self`` as positional-only
+and/or fixture parameters as keyword-only, e.g.:
+
+.. code-block:: python
+
+    class TestClass:
+
+        def test_method(self, /, *, fixture):
+            ...
+
+Before, this led to:
+
+.. code-block:: python-console
+
+    pyfuncitem = <Function test_value>
+
+        @hookimpl(trylast=True)
+        def pytest_pyfunc_call(pyfuncitem: Function) -> object | None:
+            testfunction = pyfuncitem.obj
+            if is_async_function(testfunction):
+                async_fail(pyfuncitem.nodeid)
+            funcargs = pyfuncitem.funcargs
+            testargs = {arg: funcargs[arg] for arg in pyfuncitem._fixtureinfo.argnames}
+    >       result = testfunction(**testargs)
+                 ^^^^^^^^^^^^^^^^^^^^^^^^
+    E       TypeError: TestClass.test_method() missing 1 required positional argument: 'fixture'

Diff for: src/_pytest/compat.py

@@ -122,7 +122,7 @@ def getfuncargnames(
     # creates a tuple of the names of the parameters that don't have
     # defaults.
     try:
-        parameters = signature(function).parameters
+        parameters = signature(function).parameters.values()
     except (ValueError, TypeError) as e:
         from _pytest.outcomes import fail
 
@@ -133,7 +133,7 @@ def getfuncargnames(
 
     arg_names = tuple(
         p.name
-        for p in parameters.values()
+        for p in parameters
         if (
             p.kind is Parameter.POSITIONAL_OR_KEYWORD
             or p.kind is Parameter.KEYWORD_ONLY
@@ -144,9 +144,9 @@ def getfuncargnames(
         name = function.__name__
 
     # If this function should be treated as a bound method even though
-    # it's passed as an unbound method or function, remove the first
-    # parameter name.
-    if (
+    # it's passed as an unbound method or function, and its first parameter
+    # wasn't defined as positional only, remove the first parameter name.
+    if not any(p.kind is Parameter.POSITIONAL_ONLY for p in parameters) and (
         # Not using `getattr` because we don't want to resolve the staticmethod.
         # Not using `cls.__dict__` because we want to check the entire MRO.
         cls

Diff for: testing/python/fixtures.py

@@ -48,7 +48,23 @@ class A:
         def f(self, arg1, arg2="hello"):
             raise NotImplementedError()
 
+        def g(self, /, arg1, arg2="hello"):
+            raise NotImplementedError()
+
+        def h(self, *, arg1, arg2="hello"):
+            raise NotImplementedError()
+
+        def j(self, arg1, *, arg2, arg3="hello"):
+            raise NotImplementedError()
+
+        def k(self, /, arg1, *, arg2, arg3="hello"):
+            raise NotImplementedError()
+
     assert getfuncargnames(A().f) == ("arg1",)
+    assert getfuncargnames(A().g) == ("arg1",)
+    assert getfuncargnames(A().h) == ("arg1",)
+    assert getfuncargnames(A().j) == ("arg1", "arg2")
+    assert getfuncargnames(A().k) == ("arg1", "arg2")
 
 
 def test_getfuncargnames_staticmethod():