A little unittest refactoring (#16704)

A little unittest refactoring

* Add a class decorator to generate tests when using a unittest.TestCase base class
* Add a TestCase subclass with setUp() and tearDown() that sets up
  module parameter parsing
* Move test_safe_eval to use the class decorator and ModuleTestCase base
  class
* Move testing of set_mode_if_different into its own file and separate
  some test methods out so we get better errors and more coverage in
  case of errors.
* Naming convention for test cases doesn't need to duplicate information
  that's already in the file path.

test/units/mock/procenv.py

@@ -1,4 +1,5 @@
 # (c) 2016, Matt Davis <mdavis@ansible.com>
+# (c) 2016, Toshio Kuratomi <tkuratomi@ansible.com>
 #
 # This file is part of Ansible
 #
@@ -20,10 +21,12 @@ from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
 import sys
+import json
 
 from contextlib import contextmanager
 from io import BytesIO, StringIO
 from ansible.compat.six import PY3
+from ansible.compat.tests import unittest
 from ansible.utils.unicode import to_bytes
 
 @contextmanager
@@ -54,4 +57,19 @@ def swap_stdout():
     fake_stream = BytesIO()
     sys.stdout = fake_stream
     yield fake_stream
-    sys.stdout = old_stdout
+    sys.stdout = old_stdout
+
+class ModuleTestCase(unittest.TestCase):
+    def setUp(self, module_args=None):
+        if module_args is None:
+            module_args = {}
+
+        args = json.dumps(dict(ANSIBLE_MODULE_ARGS=module_args))
+
+        # unittest doesn't have a clean place to use a context manager, so we have to enter/exit manually
+        self.stdin_swap = swap_stdin_and_argv(stdin_data=args)
+        self.stdin_swap.__enter__()
+
+    def tearDown(self):
+        # unittest doesn't have a clean place to use a context manager, so we have to enter/exit manually
+        self.stdin_swap.__exit__(None, None, None)