Refactor the way that TestApi works so that it is actually useful.

scripts/slave/annotated_run.py

Index: scripts/slave/annotated_run.py
diff --git a/scripts/slave/annotated_run.py b/scripts/slave/annotated_run.py
index e8840a870206d70d382ebf76466ca3510417934d..0e44356e68b9965a4a815beef79309af6b9bba38 100755
--- a/scripts/slave/annotated_run.py
+++ b/scripts/slave/annotated_run.py
@@ -382,8 +382,8 @@ def run_steps(stream, build_properties, factory_properties,
     properties = factory_properties.copy()
     properties.update(build_properties)
     stream.emit('Running recipe with %s' % (properties,))
-    steps = recipe_module.GenSteps(api(recipe_module.DEPS,
-                                       mod_dirs=MODULE_DIRS,
+    steps = recipe_module.GenSteps(api(MODULE_DIRS,
+                                       recipe_module.DEPS,
                                        properties=properties,
                                        step_history=step_history))
     assert inspect.isgenerator(steps)
@@ -400,7 +400,12 @@ def run_steps(stream, build_properties, factory_properties,
       step_history[step['name']] = step_result
       continue
 
-    test_data_item = test_data.pop(step['name'], {}) if test_mode else None
+    test_data_item = None
+    mock_fn = step.pop('mock_fn', None)
+    if test_mode:
+      test_data_item = mock_fn() if mock_fn else {}
+      test_data_item.update(test_data.pop(step['name'], {}))
+
     placeholders = render_step(step, test_data_item)
 
     assert step['name'] not in step_history, (