Underscores are unnecessary in pytest fixtures

deps/tests/bump/main/output/requirements.txt

@@ -1 +1 @@
-click==8.3.1
+click==8.3.2

pytest/fixture_names.py

@@ -0,0 +1,83 @@
+import ast
+import sys
+
+
+class FixtureNameChecker(ast.NodeVisitor):
+    def __init__(self, filename, source_lines):
+        self.filename = filename
+        self.source_lines = source_lines
+        self.issues = []
+        self.pytest_aliases: set[str] = set()   # names where name.fixture is the decorator
+        self.fixture_aliases: set[str] = set()  # names that *are* pytest.fixture
+
+    def visit_Import(self, node):
+        for alias in node.names:
+            if alias.name == "pytest":
+                self.pytest_aliases.add(alias.asname or alias.name)
+        self.generic_visit(node)
+
+    def visit_ImportFrom(self, node):
+        if node.module == "pytest":
+            for alias in node.names:
+                if alias.name == "fixture":
+                    self.fixture_aliases.add(alias.asname or alias.name)
+        self.generic_visit(node)
+
+    def _is_fixture_decorator(self, decorator):
+        # Unwrap call: @pytest.fixture() or @pytest.fixture(autouse=True)
+        if isinstance(decorator, ast.Call):
+            decorator = decorator.func
+        # @pytest.fixture  or  @pt.fixture
+        if (
+            isinstance(decorator, ast.Attribute)
+            and decorator.attr == "fixture"
+            and isinstance(decorator.value, ast.Name)
+            and decorator.value.id in self.pytest_aliases
+        ):
+            return True
+        # @fixture  or  @fx
+        if isinstance(decorator, ast.Name) and decorator.id in self.fixture_aliases:
+            return True
+        return False
+
+    def _check_function(self, node):
+        if node.name.startswith("_") and any(
+            self._is_fixture_decorator(d) for d in node.decorator_list
+        ):
+            # Find the name's column in the source line — more reliable than +4
+            # and handles 'async def' correctly (col_offset points to 'async').
+            line = self.source_lines[node.lineno - 1]
+            name_col = line.index(node.name, node.col_offset)
+            self.issues.append((node.lineno, name_col, node.name))
+
+    def visit_FunctionDef(self, node):
+        self._check_function(node)
+        self.generic_visit(node)
+
+    def visit_AsyncFunctionDef(self, node):
+        self._check_function(node)
+        self.generic_visit(node)
+
+
+def main(filenames):
+    exit_status = 0
+    for filename in filenames:
+        with open(filename, "rb") as f:
+            source = f.read()
+        try:
+            tree = ast.parse(source, filename=filename)
+        except SyntaxError:
+            continue
+        source_lines = source.decode("utf-8", errors="replace").splitlines()
+        checker = FixtureNameChecker(filename, source_lines)
+        checker.visit(tree)
+        for lineno, col, name in checker.issues:
+            print(
+                f"{filename}:{lineno}:{col}: no need to make things look private in tests: '{name}'"
+            )
+            exit_status = 99
+    sys.exit(exit_status)
+
+
+if __name__ == "__main__":
+    main(sys.argv[1:])

pytest/ick.toml

@@ -4,3 +4,9 @@ impl = "python"
 scope = "file"
 inputs = ["*.py"]
 deps = ["fixit", "libcst"]
+
+[[rule]]
+name = "fixture_names"
+impl = "python"
+scope = "file"
+inputs = ["tests/*.py"]

pytest/tests/fixture_names/main/input/test_example.py

@@ -0,0 +1,57 @@
+import pytest
+from pytest import fixture
+import pytest as pt
+from pytest import fixture as fx
+
+
+# Bad: leading underscore with @pytest.fixture (attribute form)
+@pytest.fixture
+def _plain_fixture():
+    pass
+
+
+# Bad: called with no args
+@pytest.fixture()
+def _called_fixture():
+    pass
+
+
+# Bad: called with autouse=True
+@pytest.fixture(autouse=True)
+def _autouse_fixture():
+    pass
+
+
+# Bad: from-import form
+@fixture
+def _direct_fixture():
+    pass
+
+
+# Bad: aliased module import
+@pt.fixture
+def _aliased_module_fixture():
+    pass
+
+
+# Bad: aliased direct import
+@fx
+def _aliased_direct_fixture():
+    pass
+
+
+# Bad: async fixture
+@pytest.fixture
+async def _async_fixture():
+    pass
+
+
+# Good: no underscore
+@pytest.fixture
+def plain_fixture():
+    pass
+
+
+# Good: underscore but no fixture decorator
+def _helper():
+    pass

pytest/tests/fixture_names/main/output/output.txt

@@ -0,0 +1,7 @@
+test_example.py:9:4: no need to make things look private in tests: '_plain_fixture'
+test_example.py:15:4: no need to make things look private in tests: '_called_fixture'
+test_example.py:21:4: no need to make things look private in tests: '_autouse_fixture'
+test_example.py:27:4: no need to make things look private in tests: '_direct_fixture'
+test_example.py:33:4: no need to make things look private in tests: '_aliased_module_fixture'
+test_example.py:39:4: no need to make things look private in tests: '_aliased_direct_fixture'
+test_example.py:45:10: no need to make things look private in tests: '_async_fixture'