fix(generative_ai): update testcase (#10944)

* fix(generative_ai): update testcase

* fix(generative_ai): add docs for test function

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* fix(generative_ai): add docs for test function

* fix(generative_ai): code reformatting

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

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generative_ai/code_completion_test_function_test.py

@@ -21,4 +21,9 @@
 @backoff.on_exception(backoff.expo, ResourceExhausted, max_time=10)
 def test_code_completion_test_function() -> None:
     content = code_completion_test_function.complete_test_function(temperature=0).text
-    assert "-> None:" in content
+    # every function def ends with `:`
+    assert content.startswith(":")
+    # test functions use `assert` for validations
+    assert "assert" in content
+    # test function should `reverse_string` at-least once
+    assert "reverse_string" in content