Improve error for mistaken self fixture

changelog/12907.improvement.rst

@@ -0,0 +1 @@
+The missing fixture error for bare test functions which mistakenly declare a ``self`` parameter now suggests removing it.

src/_pytest/fixtures.py

@@ -1009,6 +1009,11 @@ def formatrepr(self) -> FixtureLookupErrorRepr:
                 )
             else:
                 msg = f"fixture '{self.argname}' not found"
+                if self.argname == "self":
+                    msg += (
+                        "\n hint: remove 'self' from the function definition if this "
+                        "is not a method"
+                    )
             msg += "\n available fixtures: {}".format(", ".join(sorted(available)))
             msg += "\n use 'pytest --fixtures [testpath]' for help on them."
 

testing/python/fixtures.py

@@ -687,6 +687,23 @@ def test_lookup_error(unknown):
         )
         result.stdout.no_fnmatch_line("*INTERNAL*")
 
+    def test_funcarg_lookup_error_self_hint(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """
+            def test_something(self):
+                pass
+            """
+        )
+        result = pytester.runpytest()
+        result.stdout.fnmatch_lines(
+            [
+                "*ERROR at setup of test_something*",
+                "E       fixture 'self' not found",
+                ">       hint: remove 'self' from the function definition if this is not a method",
+            ]
+        )
+        result.assert_outcomes(errors=1)
+
     def test_fixture_excinfo_leak(self, pytester: Pytester) -> None:
         # on python2 sys.excinfo would leak into fixture executions
         pytester.makepyfile(