Create a fresh test class instance for each rerun

CHANGES.rst

@@ -13,6 +13,12 @@ Bug fixes
   teardown was ignored and the test was rerun anyway.
   Fixes `#270 <https://github.com/pytest-dev/pytest-rerunfailures/issues/270>`_.
 
+- Create a new test class instance for each rerun. Previously the instance of
+  the failed attempt was reused, so state stored on ``self`` leaked into the
+  rerun and broke test isolation. Fixtures cached at class scope or higher are
+  still not re-executed.
+  Fixes `#268 <https://github.com/pytest-dev/pytest-rerunfailures/issues/268>`_.
+
 Features
 ++++++++
 

src/pytest_rerunfailures.py

@@ -358,6 +358,24 @@ def _remove_cached_results_from_failed_fixtures(item):
                         fixture_def._finalizers.clear()
 
 
+def _discard_test_class_instance(item):
+    """
+    Drop the cached test class instance so the rerun gets a fresh one.
+
+    Note: pytest creates one instance per test item and caches it on the item,
+    so without this the rerun would reuse the instance -- and therefore any
+    state stored on ``self`` -- of the attempt that just failed.
+    """
+    if getattr(item, "_instance", None) is None:
+        # no instance is cached: not a test method, or pytest dropped it itself
+        return
+
+    # ``obj`` is the method bound to the cached instance, so it has to go too;
+    # both are recomputed lazily on next access.
+    del item._instance
+    item._obj = None
+
+
 def _remove_failed_setup_state_from_session(item):
     """
     Clean up setup state.
@@ -947,6 +965,7 @@ def pytest_runtest_protocol(item, nextitem):
                 # cleanin item's cashed results from any level of setups
                 _remove_cached_results_from_failed_fixtures(item)
                 _remove_failed_setup_state_from_session(item)
+                _discard_test_class_instance(item)
                 _remove_failed_subtests_from_report(item, report)
                 _remove_failed_subtest_reports_from_stats(item)
 

tests/test_pytest_rerunfailures.py

@@ -731,6 +731,75 @@ def test_pass_2(self, session_fixture, setup_fixture):
     assert_outcomes(result, passed=2, rerun=1)
 
 
+def test_rerun_recreates_test_class_instance(testdir):
+    """
+    Case: state stored on ``self`` by a failed attempt must not leak into the
+    rerun, i.e. every attempt gets a fresh test class instance
+    """
+    testdir.makepyfile(
+        """
+        import pytest
+
+        attempts = 0
+
+        class TestFoo(object):
+            @pytest.fixture(autouse=True)
+            def counting_fixture(self):
+                assert not hasattr(self, 'seen_by_fixture')
+                self.seen_by_fixture = True
+
+            @pytest.mark.flaky(reruns=2)
+            def test_fresh_instance(self):
+                global attempts
+                attempts += 1
+                assert not hasattr(self, 'seen_by_test')
+                self.seen_by_test = True
+                assert attempts == 3"""
+    )
+    result = testdir.runpytest()
+    assert_outcomes(result, passed=1, rerun=2)
+
+
+def test_rerun_recreates_instance_without_re_executing_scoped_fixtures(testdir):
+    """
+    Case: recreating the test class instance for a rerun must not invalidate
+    fixtures cached at a higher scope than function
+    """
+    testdir.makepyfile(
+        """
+        import pytest
+
+        attempts = 0
+        executions = {'session': 0, 'module': 0, 'class': 0}
+
+        @pytest.fixture(scope='session')
+        def session_fixture():
+            executions['session'] += 1
+
+        @pytest.fixture(scope='module')
+        def module_fixture():
+            executions['module'] += 1
+
+        @pytest.fixture(scope='class')
+        def class_fixture():
+            executions['class'] += 1
+
+        class TestFoo(object):
+            @pytest.mark.flaky(reruns=2)
+            def test_fresh_instance(
+                self, session_fixture, module_fixture, class_fixture
+            ):
+                global attempts
+                attempts += 1
+                assert executions == {'session': 1, 'module': 1, 'class': 1}
+                assert not hasattr(self, 'seen_by_test')
+                self.seen_by_test = True
+                assert attempts == 3"""
+    )
+    result = testdir.runpytest()
+    assert_outcomes(result, passed=1, rerun=2)
+
+
 def test_execution_count_exposed(testdir):
     testdir.makepyfile("def test_pass(): assert True")
     testdir.makeconftest(