Fixed #17365, #17366, #18727 -- Switched to discovery test runner.

Thanks to Preston Timmons for the bulk of the work on the patch, especially
updating Django's own test suite to comply with the requirements of the new
runner. Thanks also to Jannis Leidel and Mahdi Yusuf for earlier work on the
patch and the discovery runner.

Refs #11077, #17032, and #18670.

django/test/testcases.py

@@ -97,6 +97,12 @@ def assert_and_parse_html(self, html, user_msg, msg):
 
 
 class OutputChecker(doctest.OutputChecker):
+    def __init__(self):
+        warnings.warn(
+            "The django.test.testcases.OutputChecker class is deprecated; "
+            "use the doctest module from the Python standard library instead.",
+            PendingDeprecationWarning)
+
     def check_output(self, want, got, optionflags):
         """
         The entry method for doctest output checking. Defers to a sequence of
@@ -151,6 +157,10 @@ class OutputChecker(doctest.OutputChecker):
 
 class DocTestRunner(doctest.DocTestRunner):
     def __init__(self, *args, **kwargs):
+        warnings.warn(
+            "The django.test.testcases.DocTestRunner class is deprecated; "
+            "use the doctest module from the Python standard library instead.",
+            PendingDeprecationWarning)
         doctest.DocTestRunner.__init__(self, *args, **kwargs)
         self.optionflags = doctest.ELLIPSIS