unittest's unexpectedSuccess should work as non-strict xpass

Make sure tests for that behavior obtain the same return code
using either pytest or unittest to run the same file

_pytest/skipping.py

@@ -220,6 +220,18 @@ def check_strict_xfail(pyfuncitem):
             pytest.fail('[XPASS(strict)] ' + explanation, pytrace=False)
 
 
+def _is_unittest_unexpected_success_a_failure():
+    """Return if the test suite should fail if a @expectedFailure unittest test PASSES.
+
+    From https://docs.python.org/3/library/unittest.html?highlight=unittest#unittest.TestResult.wasSuccessful:
+        Changed in version 3.4: Returns False if there were any
+        unexpectedSuccesses from tests marked with the expectedFailure() decorator.
+
+    TODO: this should be moved to the "compat" module.
+    """
+    return sys.version_info >= (3, 4)
+
+
 @pytest.hookimpl(hookwrapper=True)
 def pytest_runtest_makereport(item, call):
     outcome = yield
@@ -228,13 +240,15 @@ def pytest_runtest_makereport(item, call):
     evalskip = getattr(item, '_evalskip', None)
     # unitttest special case, see setting of _unexpectedsuccess
     if hasattr(item, '_unexpectedsuccess') and rep.when == "call":
-        # unittest treats an 'unexpected successes' as a failure
-        # which means pytest needs to handle it like a 'xfail(strict=True)'
-        rep.outcome = "failed"
         if item._unexpectedsuccess:
             rep.longrepr = "Unexpected success: {0}".format(item._unexpectedsuccess)
         else:
             rep.longrepr = "Unexpected success"
+        if _is_unittest_unexpected_success_a_failure():
+            rep.outcome = "failed"
+        else:
+            rep.outcome = "passed"
+            rep.wasxfail = rep.longrepr
     elif item.config.option.runxfail:
         pass   # don't interefere
     elif call.excinfo and call.excinfo.errisinstance(pytest.xfail.Exception):

testing/test_unittest.py

@@ -419,8 +419,9 @@ class TestTrialUnittest:
                 def test_method(self):
                     pass
         """)
+        from _pytest.skipping import _is_unittest_unexpected_success_a_failure
+        should_fail = _is_unittest_unexpected_success_a_failure()
         result = testdir.runpytest("-rxs")
-        assert result.ret == 0
         result.stdout.fnmatch_lines_random([
             "*XFAIL*test_trial_todo*",
             "*trialselfskip*",
@@ -429,8 +430,9 @@ class TestTrialUnittest:
             "*i2wanto*",
             "*sys.version_info*",
             "*skip_in_method*",
-            "*4 skipped*3 xfail*1 xpass*",
+            "*1 failed*4 skipped*3 xfailed*" if should_fail else "*4 skipped*3 xfail*1 xpass*",
         ])
+        assert result.ret == (1 if should_fail else 0)
 
     def test_trial_error(self, testdir):
         testdir.makepyfile("""
@@ -587,39 +589,62 @@ def test_unittest_typerror_traceback(testdir):
     assert "TypeError" in result.stdout.str()
     assert result.ret == 1
 
+
 @pytest.mark.skipif("sys.version_info < (2,7)")
-def test_unittest_expected_failure_for_failing_test_is_xfail(testdir):
-    testdir.makepyfile("""
+@pytest.mark.parametrize('runner', ['pytest', 'unittest'])
+def test_unittest_expected_failure_for_failing_test_is_xfail(testdir, runner):
+    script = testdir.makepyfile("""
         import unittest
         class MyTestCase(unittest.TestCase):
             @unittest.expectedFailure
             def test_failing_test_is_xfail(self):
                 assert False
+        if __name__ == '__main__':
+            unittest.main()
     """)
-    result = testdir.runpytest("-rxX")
-    result.stdout.fnmatch_lines([
-        "*XFAIL*MyTestCase*test_failing_test_is_xfail*",
-        "*1 xfailed*",
-    ])
+    if runner == 'pytest':
+        result = testdir.runpytest("-rxX")
+        result.stdout.fnmatch_lines([
+            "*XFAIL*MyTestCase*test_failing_test_is_xfail*",
+            "*1 xfailed*",
+        ])
+    else:
+        result = testdir.runpython(script)
+        result.stderr.fnmatch_lines([
+            "*1 test in*",
+            "*OK*(expected failures=1)*",
+        ])
     assert result.ret == 0
 
+
 @pytest.mark.skipif("sys.version_info < (2,7)")
-def test_unittest_expected_failure_for_passing_test_is_fail(testdir):
-    testdir.makepyfile("""
+@pytest.mark.parametrize('runner', ['pytest', 'unittest'])
+def test_unittest_expected_failure_for_passing_test_is_fail(testdir, runner):
+    script = testdir.makepyfile("""
         import unittest
         class MyTestCase(unittest.TestCase):
             @unittest.expectedFailure
             def test_passing_test_is_fail(self):
                 assert True
+        if __name__ == '__main__':
+            unittest.main()
     """)
-    result = testdir.runpytest("-rxX")
-    result.stdout.fnmatch_lines([
-        "*FAILURES*",
-        "*MyTestCase*test_passing_test_is_fail*",
-        "*Unexpected success*",
-        "*1 failed*",
-    ])
-    assert result.ret == 1
+    from _pytest.skipping import _is_unittest_unexpected_success_a_failure
+    should_fail = _is_unittest_unexpected_success_a_failure()
+    if runner == 'pytest':
+        result = testdir.runpytest("-rxX")
+        result.stdout.fnmatch_lines([
+            "*MyTestCase*test_passing_test_is_fail*",
+            "*1 failed*" if should_fail else "*1 xpassed*",
+        ])
+    else:
+        result = testdir.runpython(script)
+        result.stderr.fnmatch_lines([
+            "*1 test in*",
+            "*(unexpected successes=1)*",
+        ])
+
+    assert result.ret == (1 if should_fail else 0)
 
 
 @pytest.mark.parametrize('fix_type, stmt', [