Add initial postprocess unit test thingy.

recipes/engine_tests/whitelist_steps.py

 # Copyright 2015 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 """Tests that step_data can accept multiple specs at once."""
 
+from recipe_engine.recipe_api import Property
+from recipe_engine.post_process import Filter, DoesNotRun, MustRun
+
 DEPS = [
   'step',
+  'properties',
 ]
 
-def RunSteps(api):
+PROPERTIES = {
+  'fakeit': Property(kind=bool, default=True),
+}
+
+def RunSteps(api, fakeit):
   api.step('something unimportant', ['echo', 'sup doc'])
   api.step('something important', ['echo', 'crazy!'], env={'FLEEM': 'VERY YES'})
   api.step('another important', ['echo', 'INSANITY'])
+  if fakeit:
+    api.step('fakestep', ['echo', 'FAAAAKE'])
+
 
 def GenTests(api):
-  yield api.test('all_steps')
+  yield api.test('all_steps') + api.post_process(MustRun, 'fakestep')
 
   yield (api.test('single_step')
-    + api.whitelist('something important')
+    + api.post_process(Filter('something important'))
   )
 
   yield (api.test('two_steps')
-    + api.whitelist('something important')
-    + api.whitelist('another important')
+    + api.post_process(Filter('something important', 'another important'))
   )
 
+  f = Filter()
+  f = f.include('another important', ['cmd'])
+  f = f.include('something important', ['env'])
   yield (api.test('selection')
-    + api.whitelist('something important', 'env')
-    + api.whitelist('another important', 'cmd')
+    + api.properties(fakeit=False)
+    + api.post_process(DoesNotRun, 'fakestep')
+    + api.post_process(f)
   )
 
-  yield (api.test('result')
-    + api.whitelist('$result')
-  )
+  yield api.test('result') + api.post_process(Filter('$result'))