unittest: do not use TestCase.debug() with `--pdb`

Fixes https://github.com/pytest-dev/pytest/issues/5991
Fixes https://github.com/pytest-dev/pytest/issues/3823

Ref: https://github.com/pytest-dev/pytest-django/issues/772
Ref: https://github.com/pytest-dev/pytest/pull/1890
Ref: https://github.com/pytest-dev/pytest-django/pull/782

- inject wrapped testMethod

- adjust test_trial_error

- add test for `--trace` with unittests

changelog/3823.bugfix.rst

@@ -0,0 +1 @@
+``--trace`` now works with unittests.

changelog/5991.bugfix.rst

@@ -0,0 +1 @@
+Fix interaction with ``--pdb`` and unittests: do not use unittest's ``TestCase.debug()``.

doc/en/unittest.rst

@@ -238,17 +238,6 @@ was executed ahead of the ``test_method``.
 
 .. _pdb-unittest-note:
 
-.. note::
-
-    Running tests from ``unittest.TestCase`` subclasses with ``--pdb`` will
-    disable tearDown and cleanup methods for the case that an Exception
-    occurs. This allows proper post mortem debugging for all applications
-    which have significant logic in their tearDown machinery. However,
-    supporting this feature has the following side effect: If people
-    overwrite ``unittest.TestCase`` ``__call__`` or ``run``, they need to
-    to overwrite ``debug`` in the same way  (this is also true for standard
-    unittest).
-
 .. note::
 
     Due to architectural differences between the two frameworks, setup and

src/_pytest/unittest.py

@@ -1,4 +1,5 @@
 """ discovery and running of std-library "unittest" style tests. """
+import functools
 import sys
 import traceback
 
@@ -107,6 +108,7 @@ class TestCaseFunction(Function):
     nofuncargs = True
     _excinfo = None
     _testcase = None
+    _need_tearDown = None
 
     def setup(self):
         self._testcase = self.parent.obj(self.name)
@@ -115,6 +117,8 @@ class TestCaseFunction(Function):
             self._request._fillfixtures()
 
     def teardown(self):
+        if self._need_tearDown:
+            self._testcase.tearDown()
         self._testcase = None
         self._obj = None
 
@@ -187,29 +191,45 @@ class TestCaseFunction(Function):
     def stopTest(self, testcase):
         pass
 
-    def _handle_skip(self):
-        # implements the skipping machinery (see #2137)
-        # analog to pythons Lib/unittest/case.py:run
-        testMethod = getattr(self._testcase, self._testcase._testMethodName)
-        if getattr(self._testcase.__class__, "__unittest_skip__", False) or getattr(
-            testMethod, "__unittest_skip__", False
-        ):
-            # If the class or method was skipped.
-            skip_why = getattr(
-                self._testcase.__class__, "__unittest_skip_why__", ""
-            ) or getattr(testMethod, "__unittest_skip_why__", "")
-            self._testcase._addSkip(self, self._testcase, skip_why)
-            return True
-        return False
-
     def runtest(self):
-        if self.config.pluginmanager.get_plugin("pdbinvoke") is None:
+        testMethod = getattr(self._testcase, self._testcase._testMethodName)
+
+        class _GetOutOf_testPartExecutor(KeyboardInterrupt):
+            """Helper exception to get out of unittests's testPartExecutor."""
+
+        unittest = sys.modules.get("unittest")
+
+        reraise = ()
+        if unittest:
+            reraise += (unittest.SkipTest,)
+
+        @functools.wraps(testMethod)
+        def wrapped_testMethod(*args, **kwargs):
+            try:
+                self.ihook.pytest_pyfunc_call(pyfuncitem=self)
+            except reraise:
+                raise
+            except Exception as exc:
+                expecting_failure_method = getattr(
+                    testMethod, "__unittest_expecting_failure__", False
+                )
+                expecting_failure_class = getattr(
+                    self, "__unittest_expecting_failure__", False
+                )
+                expecting_failure = expecting_failure_class or expecting_failure_method
+                self._need_tearDown = True
+
+                if expecting_failure:
+                    raise
+
+                raise _GetOutOf_testPartExecutor(exc)
+
+        self._testcase._wrapped_testMethod = wrapped_testMethod
+        self._testcase._testMethodName = "_wrapped_testMethod"
+        try:
             self._testcase(result=self)
-        else:
+        except _GetOutOf_testPartExecutor as exc:
-            # disables tearDown and cleanups for post mortem debugging (see #1890)
+            raise exc.args[0] from exc.args[0]
-            if self._handle_skip():
-                return
-            self._testcase.debug()
 
     def _prunetraceback(self, excinfo):
         Function._prunetraceback(self, excinfo)

testing/test_unittest.py

@@ -537,24 +537,28 @@ class TestTrialUnittest:
         )
         result.stdout.fnmatch_lines(
             [
-                "test_trial_error.py::TC::test_four FAILED",
+                "test_trial_error.py::TC::test_four SKIPPED",
                 "test_trial_error.py::TC::test_four ERROR",
                 "test_trial_error.py::TC::test_one FAILED",
                 "test_trial_error.py::TC::test_three FAILED",
-                "test_trial_error.py::TC::test_two FAILED",
+                "test_trial_error.py::TC::test_two SKIPPED",
+                "test_trial_error.py::TC::test_two ERROR",
                 "*ERRORS*",
                 "*_ ERROR at teardown of TC.test_four _*",
+                "NOTE: Incompatible Exception Representation, displaying natively:",
+                "*DelayedCalls*",
+                "*_ ERROR at teardown of TC.test_two _*",
+                "NOTE: Incompatible Exception Representation, displaying natively:",
                 "*DelayedCalls*",
                 "*= FAILURES =*",
-                "*_ TC.test_four _*",
+                # "*_ TC.test_four _*",
-                "*NameError*crash*",
+                # "*NameError*crash*",
                 "*_ TC.test_one _*",
                 "*NameError*crash*",
                 "*_ TC.test_three _*",
+                "NOTE: Incompatible Exception Representation, displaying natively:",
                 "*DelayedCalls*",
-                "*_ TC.test_two _*",
+                "*= 2 failed, 2 skipped, 2 errors in *",
-                "*NameError*crash*",
-                "*= 4 failed, 1 error in *",
             ]
         )
 
@@ -1096,3 +1100,32 @@ def test_exit_outcome(testdir):
     )
     result = testdir.runpytest()
     result.stdout.fnmatch_lines(["*Exit: pytest_exit called*", "*= no tests ran in *"])
+
+
+def test_trace(testdir, monkeypatch):
+    calls = []
+
+    def check_call(*args, **kwargs):
+        calls.append((args, kwargs))
+        assert args == ("runcall",)
+
+        class _pdb:
+            def runcall(*args, **kwargs):
+                calls.append((args, kwargs))
+
+        return _pdb
+
+    monkeypatch.setattr("_pytest.debugging.pytestPDB._init_pdb", check_call)
+
+    p1 = testdir.makepyfile(
+        """
+        import unittest
+
+        class MyTestCase(unittest.TestCase):
+            def test(self):
+                self.assertEqual('foo', 'foo')
+    """
+    )
+    result = testdir.runpytest("--trace", str(p1))
+    assert len(calls) == 2
+    assert result.ret == 0