Mock return values and side effects in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a mock return value in pytest?

A mock return value is a preset value that a mocked function returns when called during a test. It helps simulate behavior without running the real code.

intermediate

What does the side_effect attribute do in a pytest mock?

The side_effect attribute lets you define custom behavior for a mock, like raising exceptions or returning different values on each call.

intermediate

How do you set a mock to return different values on consecutive calls?

Use side_effect with a list of values. Each call to the mock returns the next value in the list.

beginner

Example: What will this mock return on the first and second call?

mocked_function.side_effect = [10, 20]

On the first call, it returns 10. On the second call, it returns 20. After that, it raises StopIteration.

intermediate

Why use side_effect to raise an exception in a mock?

To test how your code handles errors without causing real failures. It simulates exceptions from dependencies.

In pytest, how do you set a mock to always return the value 5?

A mock.return_value = 5

B mock.side_effect = 5

C mock.return = 5

D mock.value = 5

Use return_value to set a fixed return value for the mock.

What happens if side_effect is set to a list of values?

A The mock returns values from the list on each call, then raises StopIteration.

B The mock always returns the whole list.

C The mock raises an exception immediately.

D The mock ignores the list and returns None.

side_effect as a list makes the mock return each value in order, then raises StopIteration when exhausted.

How can you simulate an exception being raised by a mock?

A Set side_effect to the exception class or instance.

B Set return_value to the exception.

C Call mock.raise_exception()

D Set mock.error = True

Setting side_effect to an exception causes the mock to raise it when called.

Which attribute would you use to make a mock return different values on multiple calls?

A side_effect

B return_value

C call_count

D mock_values

side_effect can be a list to return different values on each call.

If you want a mock to behave like a function that sometimes raises an error, what should you do?

A Use side_effect with a function that raises the error conditionally.

B Set return_value to None.

C Set side_effect to a list of only values.

D Use return_value with an error message.

side_effect can be a function that raises exceptions or returns values based on logic.

Explain how to use mock return_value and side_effect in pytest to control mock behavior.

Think about how to simulate normal and error cases with mocks.

Describe a real-life scenario where you would use side_effect to raise an exception in a mock.

Imagine testing how your app reacts when a service is down.