Make git.checkout return the commit hash.

recipe_modules/git/example.py

Index: recipe_modules/git/example.py
diff --git a/recipe_modules/git/example.py b/recipe_modules/git/example.py
index dc9fe0a8772dbb46fceabadc4ab42432e4b8677e..e86791863d12087430860b750d212b680c2a85f1 100644
--- a/recipe_modules/git/example.py
+++ b/recipe_modules/git/example.py
@@ -26,18 +26,24 @@ def RunSteps(api):
           True)
 
   # You can use api.git.checkout to perform all the steps of a safe checkout.
-  api.git.checkout(
+  set_got_revision=api.properties.get('set_got_revision')
+  retVal = api.git.checkout(
       url,
       ref=api.properties.get('revision'),
       recursive=True,
       submodule_update_force=submodule_update_force,
-      set_got_revision=api.properties.get('set_got_revision'),
+      set_got_revision=set_got_revision,
       curl_trace_file=curl_trace_file,
       remote_name=api.properties.get('remote_name'),
       display_fetch_size=api.properties.get('display_fetch_size'),
       file_name=api.properties.get('checkout_file_name'),
       submodule_update_recursive=submodule_update_recursive)
 
+  if set_got_revision:
+    assert retVal == api.properties['expected_got_revision'], (
+      "expected retVal to be %r but was %r" % (
+        api.properties['expected_got_revision'], retVal))
+
   # count_objects shows number and size of objects in .git dir.
   api.git.count_objects(
       name='count-objects',
@@ -107,7 +113,10 @@ def GenTests(api):
 
   yield (
       api.test('set_got_revision') +
-      api.properties(set_got_revision=True) +
+      api.properties(
+        set_got_revision=True,
+        expected_got_revision="deadbeef",
+      ) +
       api.step_data('set got_revision',
                     stdout=api.raw_io.output('deadbeef'))
   )