Ability to define custom test_runner for django test runner class

Move test_runner kwargs generation into separate method, like in django 1.11+ (still working in prior versions)
Use `test_runner` attribute instead of hardcoded `xmlrunner.XMLTestRunner`

Author: Nnonexistent

xmlrunner/extra/djangotestrunner.py

@@ -17,27 +17,47 @@
 
 
 class XMLTestRunner(DiscoverRunner):
+    test_runner = xmlrunner.XMLTestRunner
 
-    def run_suite(self, suite, **kwargs):
-        dummy = kwargs  # unused
+    def get_resultclass(self):
+        # Django provides `DebugSQLTextTestResult` if `debug_sql` argument is True
+        # To use `xmlrunner.result._XMLTestResult` we supress default behavior
+        return None
+
+    def get_test_runner_kwargs(self):
+        # We use separate verbosity setting for our runner
         verbosity = getattr(settings, 'TEST_OUTPUT_VERBOSE', 1)
-        # XXX: verbosity = self.verbosity
         if isinstance(verbosity, bool):
             verbosity = (1, 2)[verbosity]
-        descriptions = getattr(settings, 'TEST_OUTPUT_DESCRIPTIONS', False)
+        verbosity = verbosity  # not self.verbosity
+
         output_dir = getattr(settings, 'TEST_OUTPUT_DIR', '.')
         single_file = getattr(settings, 'TEST_OUTPUT_FILE_NAME', None)
 
-        kwargs = dict(
-            verbosity=verbosity, descriptions=descriptions,
-            failfast=self.failfast)
+        # For single file case we are able to create file here
+        # But for multiple files case files will be created inside runner/results
         if single_file is not None:
             if not os.path.exists(output_dir):
                 os.makedirs(output_dir)
+
+        if single_file is None:  # output is a stream
+            output = output_dir
+        else:  # output is a folder
             file_path = os.path.join(output_dir, single_file)
-            with open(file_path, 'wb') as xml:
-                return xmlrunner.XMLTestRunner(
-                    output=xml, **kwargs).run(suite)
-        else:
-            return xmlrunner.XMLTestRunner(
-                output=output_dir, **kwargs).run(suite)
+            output = open(file_path, 'wb')
+
+        return dict(
+            verbosity=verbosity,
+            descriptions=getattr(settings, 'TEST_OUTPUT_DESCRIPTIONS', False),
+            failfast=self.failfast,
+            resultclass=self.get_resultclass(),
+            output=output,
+        )
+
+    def run_suite(self, suite, **kwargs):
+        kwargs = self.get_test_runner_kwargs()
+        runner = self.test_runner(**kwargs)
+        results = runner.run(suite)
+        if hasattr(kwargs['output'], 'close'):
+            kwargs['output'].close()
+        return results