Add simple depends_on API.

recipes/engine_tests/depend_on/need_return_schema.py

Index: recipes/engine_tests/depend_on/need_return_schema.py
diff --git a/recipes/engine_tests/depend_on/need_return_schema.py b/recipes/engine_tests/depend_on/need_return_schema.py
new file mode 100644
index 0000000000000000000000000000000000000000..d7f1fee336353f7611329a58d9707d9aa9ab89ba
--- /dev/null
+++ b/recipes/engine_tests/depend_on/need_return_schema.py
@@ -0,0 +1,19 @@
+from recipe_engine.recipe_api import Property
+from recipe_engine import config
+
+DEPS = [
+    'recipe_engine/properties',
+]
+
+PROPERTIES = {}
+
+# Missing a RETURN_SCHEMA on purpose
+
+def RunSteps(api):
+  api.depend_on('engine_tests/depend_on/need_return_schema_helper', {})
+
+def GenTests(api):
+  yield (
+      api.test('basic') +
+      api.expect_exception('ValueError')
+  )