Make DBTestCase compatible with pytest (#5691)

* Make DbTestCase compatible with pytest

* augment note about future enhancement for pytest support

* reformat with black

Author: cognifloyd

st2tests/st2tests/base.py

@@ -16,6 +16,8 @@
 from __future__ import absolute_import
 from __future__ import print_function
 
+from unittest.result import TestResult
+
 # NOTE: We need to perform monkeypatch before importing ssl module otherwise tests will fail.
 # See https://github.com/StackStorm/st2/pull/4834 for details
 from st2common.util.monkey_patch import monkey_patch
@@ -316,7 +318,16 @@ def setUpClass(cls):
     def tearDownClass(cls):
         drop_db = True
 
-        if cls.current_result.errors or cls.current_result.failures:
+        # TODO: pytst does not make results available to fixtures by default.
+        #       we might be able to add a hook+class fixture to help with this, but
+        #       that adds quite a bit of complexity. For now, pytest will always drop the db.
+        #       https://docs.pytest.org/en/stable/example/simple.html#making-test-result-information-available-in-fixtures
+        #       When someone does decide to tackle this, we will probably need to rename the db
+        #       for later inspection so subsequent tests still have a clean starting point as
+        #       pytest will not necessarily stop on failure like nosetest did.
+        if cls.current_result and (
+            cls.current_result.errors or cls.current_result.failures
+        ):
             # Don't drop DB on test failure
             drop_db = False
 
@@ -325,8 +336,11 @@ def tearDownClass(cls):
 
     def run(self, result=None):
         # Remember result for use in tearDown and tearDownClass
-        self.current_result = result
-        self.__class__.current_result = result
+        # pytest sets result to _pytest.unittest.TestCaseFunction
+        # which does not have attributes: errors, failures
+        if isinstance(result, TestResult):
+            self.current_result = result
+            self.__class__.current_result = result
         super(DbTestCase, self).run(result=result)