TestModelMixin: Perform stateless model creation

Don't delete test models at the end of the test case.
Failed test cases don't execute the tearDown() method.
Instead perform model registry cleanup before creating
any new test model.

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

mayan/apps/common/tests/mixins.py

@@ -234,13 +234,24 @@ class TempfileCheckTestCaseMixin(object):
 
 
 class TestModelTestMixin(object):
-    _test_models = []
-
     def _create_test_model(self, fields=None, model_name='TestModel', options=None):
+        # Obtain the app_config and app_label from the test's module path
+        app_config = apps.get_containing_app_config(
+            object_name=self.__class__.__module__
+        )
+        app_label = app_config.label
+
         class Meta:
             pass
 
+        setattr(Meta, 'app_label', app_label)
+
+        if options is not None:
+            for key, value in options.items():
+                setattr(Meta, key, value)
+
         def save(instance, *args, **kwargs):
+            # Custom .save() method to use random primary key values.
             if instance.pk:
                 return models.Model.self(instance, *args, **kwargs)
             else:
@@ -251,10 +262,6 @@ class TestModelTestMixin(object):
 
                 return instance.save_base(force_insert=True)
 
-        if options is not None:
-            for key, value in options.items():
-                setattr(Meta, key, value)
-
         attrs = {
             '__module__': self.__class__.__module__, 'save': save, 'Meta': Meta
         }
@@ -262,6 +269,11 @@ class TestModelTestMixin(object):
         if fields:
             attrs.update(fields)
 
+        # Clear previous model registration before re-registering it again to
+        # avoid conflict with test models with the same name, in the same app
+        # but from another test module.
+        apps.all_models[app_label].pop(model_name.lower(), None)
+
         TestModel = type(
             force_bytes(model_name), (models.Model,), attrs
         )
@@ -271,8 +283,6 @@ class TestModelTestMixin(object):
         with connection.schema_editor() as schema_editor:
             schema_editor.create_model(model=TestModel)
 
-        self.__class__._test_models.append(model_name)
-        apps.clear_cache()
         ContentType.objects.clear_cache()
 
     def _create_test_object(self, model_name='TestModel', **kwargs):
@@ -280,26 +290,6 @@ class TestModelTestMixin(object):
 
         self.test_object = TestModel.objects.create(**kwargs)
 
-    def _delete_test_model(self, model_name='TestModel'):
-        TestModel = getattr(self, model_name)
-
-        with connection.schema_editor() as schema_editor:
-            schema_editor.delete_model(model=TestModel)
-
-        del TestModel._meta.app_config.models[model_name.lower()]
-        apps.clear_cache()
-        ContentType.objects.clear_cache()
-
-    def _delete_test_models(self):
-        for test_model in self.__class__._test_models:
-            self._delete_test_model(model_name=test_model)
-
-        self.__class__._test_models = []
-
-    def tearDown(self):
-        self._delete_test_models()
-        super(TestModelTestMixin, self).tearDown()
-
 
 class TestViewTestCaseMixin(object):
     has_test_view = False