javascript - 模拟函数没有被 Jest 调用

Question

我正在尝试测试:

onChange(value) {
  this.setState({ postcode: value });
  if (value.length >= 3) this.listSuggestions(value);
}

通过写作:

test("onChange updates the state", () => {
  const postalCodeWrapper = mount(<PostalCode />);
  const instance = postalCodeWrapper.instance();
  const listSuggestions = jest.fn(instance.listSuggestions);

  const mockValue = "this is mock value";
  instance.onChange(mockValue);
  expect(instance.state.postcode).toBe(mockValue);
  expect(listSuggestions).toHaveBeenCalled();
});

这会返回 Expected mock function to have been called, but it was not called.，谈论listSuggestions。这是为什么？如果我删除 if (value.length >= 3) 语句，也会发生同样的事情。

Answer 1

你的问题是这一行:

const listSuggestions = jest.fn(instance.listSuggestions);

当您调用它时，jest.fn 返回一个新 函数，而不是改变现有方法。您将其分配给 const，但您的组件将调用原始组件。

将其更改为:

instance.listSuggestions = jest.fn(instance.listSuggestions);

用模拟函数覆盖组件方法，假设条件检查通过，它将调用该函数。