单元测试：解释模拟对象的有用性[重复]

Question

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What is Object Mocking and when do I need it?

Answer 1

You might indeed start writing tests for B and implementing B as soon as you know you need it and then come back to A. But when you come back to A you might want to use a mock for B so that your test for A is really testing A and its interactions with B.

Part of the reason for this is there might be another class C that B uses to do some of its work. If you want to test A using a real B, you'll also need C, and of course the difficulty can extend further.

Using mocks you can make your test check only that A calls B methods when it should and deals properly with the responses that you tell your mock to give, rather than depending on a real implementation of B.