Improve error message when TestCase functions use a parametrized fixture

Fix #2535

Author: nicoddemus

changelog/2535.bugfix.rst

@@ -0,0 +1 @@
+Improve error message when test functions of ``unittest.TestCase`` subclasses use a parametrized fixture.

src/_pytest/fixtures.py

@@ -562,7 +562,20 @@ def _compute_fixture_value(self, fixturedef):
         except (AttributeError, ValueError):
             param = NOTSET
             param_index = 0
-            if fixturedef.params is not None:
+            has_params = fixturedef.params is not None
+            fixtures_not_supported = getattr(funcitem, "nofuncargs", False)
+            if has_params and fixtures_not_supported:
+                msg = (
+                    "{name} does not support fixtures, maybe unittest.TestCase subclass?\n"
+                    "Node id: {nodeid}\n"
+                    "Function type: {typename}"
+                ).format(
+                    name=funcitem.name,
+                    nodeid=funcitem.nodeid,
+                    typename=type(funcitem).__name__,
+                )
+                fail(msg)
+            if has_params:
                 frame = inspect.stack()[3]
                 frameinfo = inspect.getframeinfo(frame[0])
                 source_path = frameinfo.filename
@@ -571,9 +584,11 @@ def _compute_fixture_value(self, fixturedef):
                 if source_path.relto(funcitem.config.rootdir):
                     source_path = source_path.relto(funcitem.config.rootdir)
                 msg = (
-                    "The requested fixture has no parameter defined for the "
-                    "current test.\n\nRequested fixture '{}' defined in:\n{}"
+                    "The requested fixture has no parameter defined for test:\n"
+                    "    {}\n\n"
+                    "Requested fixture '{}' defined in:\n{}"
                     "\n\nRequested here:\n{}:{}".format(
+                        funcitem.nodeid,
                         fixturedef.argname,
                         getlocation(fixturedef.func, funcitem.config.rootdir),
                         source_path,

testing/example_scripts/unittest/test_parametrized_fixture_error_message.py

@@ -0,0 +1,13 @@
+import pytest
+import unittest
+
+
+@pytest.fixture(params=[1, 2])
+def two(request):
+    return request.param
+
+
+@pytest.mark.usefixtures("two")
+class TestSomethingElse(unittest.TestCase):
+    def test_two(self):
+        pass

testing/python/fixture.py

@@ -3600,7 +3600,8 @@ def test_foo(request, get_named_fixture):
         result = testdir.runpytest()
         result.stdout.fnmatch_lines(
             """
-            E*Failed: The requested fixture has no parameter defined for the current test.
+            E*Failed: The requested fixture has no parameter defined for test:
+            E*    test_call_from_fixture.py::test_foo
             E*
             E*Requested fixture 'fix_with_param' defined in:
             E*test_call_from_fixture.py:4
@@ -3626,7 +3627,8 @@ def test_foo(request):
         result = testdir.runpytest()
         result.stdout.fnmatch_lines(
             """
-            E*Failed: The requested fixture has no parameter defined for the current test.
+            E*Failed: The requested fixture has no parameter defined for test:
+            E*    test_call_from_test.py::test_foo
             E*
             E*Requested fixture 'fix_with_param' defined in:
             E*test_call_from_test.py:4
@@ -3656,7 +3658,8 @@ def test_foo(request):
         result = testdir.runpytest()
         result.stdout.fnmatch_lines(
             """
-            E*Failed: The requested fixture has no parameter defined for the current test.
+            E*Failed: The requested fixture has no parameter defined for test:
+            E*    test_external_fixture.py::test_foo
             E*
             E*Requested fixture 'fix_with_param' defined in:
             E*conftest.py:4
@@ -3699,7 +3702,8 @@ def test_foo(request):
         result = testdir.runpytest()
         result.stdout.fnmatch_lines(
             """
-            E*Failed: The requested fixture has no parameter defined for the current test.
+            E*Failed: The requested fixture has no parameter defined for test:
+            E*    test_foos.py::test_foo
             E*
             E*Requested fixture 'fix_with_param' defined in:
             E*fix.py:4

testing/test_unittest.py

@@ -1010,3 +1010,15 @@ def test_hello(self):
     result = testdir.runpytest()
     assert "should raise this exception" in result.stdout.str()
     assert "ERROR at teardown of MyTestCase.test_hello" not in result.stdout.str()
+
+
+def test_error_message_with_parametrized_fixtures(testdir):
+    testdir.copy_example("unittest/test_parametrized_fixture_error_message.py")
+    result = testdir.runpytest()
+    result.stdout.fnmatch_lines(
+        [
+            "*test_two does not support fixtures*",
+            "*TestSomethingElse::test_two",
+            "*Function type: TestCaseFunction",
+        ]
+    )