Inspect test classes to avoid running setUpClass and tearDownClass

If a test class has all it's tests marked to be skipped, we mark the
class to be skipped so that `setUpClass` and `tearDownClass` doesn't
even run.

tests/support/unit.py

@@ -21,12 +21,13 @@
 """
 # pylint: disable=unused-import,blacklisted-module,deprecated-method
 
-# Import python libs
 from __future__ import absolute_import, print_function, unicode_literals
 
+import inspect
 import logging
 import os
 import sys
+import types
 from unittest import TestCase as _TestCase
 from unittest import TestLoader as _TestLoader
 from unittest import TestResult
@@ -118,6 +119,43 @@ class TestSuite(_TestSuite):
                         )
                         delattr(previousClass, attr)
 
+    def _handleModuleFixture(self, test, result):
+        # We override _handleModuleFixture so that we can inspect all test classes in the module.
+        # If all tests in a test class are going to be skipped, mark the class to skip.
+        # This avoids running setUpClass and tearDownClass unnecessarily
+        currentModule = test.__class__.__module__
+        try:
+            module = sys.modules[currentModule]
+        except KeyError:
+            return
+        for attr in dir(module):
+            klass = getattr(module, attr)
+            if not inspect.isclass(klass):
+                # Not even a class? Carry on...
+                continue
+            if klass.__module__ != currentModule:
+                # This class is not defined in the module being tested? Carry on...
+                continue
+            if not issubclass(klass, TestCase):
+                # This class is not a subclass of TestCase, carry on
+                continue
+
+            skip_klass = True
+            test_functions = [name for name in dir(klass) if name.startswith("test_")]
+            for name in test_functions:
+                func = getattr(klass, name)
+                if not isinstance(func, types.FunctionType):
+                    # Not even a function, carry on
+                    continue
+                if getattr(func, "__unittest_skip__", False) is False:
+                    # At least one test is not going to be skipped.
+                    # Stop searching.
+                    skip_klass = False
+                    break
+            if skip_klass is True:
+                klass.__unittest_skip__ = True
+        return super(TestSuite, self)._handleModuleFixture(test, result)
+
 
 class TestLoader(_TestLoader):
     # We're just subclassing to make sure tha tour TestSuite class is the one used