jest typescript 属性模拟在类型上不存在
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jest typescript property mock does not exist on type
提问by ext
When using jest.fn()to add a mock you can usually access the .mockproperty to access details such as calls, something similar to this:
使用jest.fn()添加模拟时，您通常可以访问该.mock属性以访问调用等详细信息，类似于以下内容：
test('not working', () => {
const foo = new Foo();
foo.addListener = jest.fn();
foo.func(); // will call addListener with a callback
const callback = foo.addListener.mock.calls[0][0];
expect(callback()).toEqual(1); // test the callback
});
When implementing the test in typescript instead of plain javascript I get the error:
当在打字稿而不是普通的 javascript 中实现测试时，我收到错误：
error TS2339: Property 'mock' does not exist on type '(callback: () => number) => void'.
错误 TS2339：属性 'mock' 在类型 '(callback: () => number) => void' 上不存在。
I can get rid of the error by casting to anybut surely there must be a better way:
我可以通过强制转换来摆脱错误，any但肯定有更好的方法：
const callback = (foo.addListener as any).mock.calls[0][0];
In this simple code the mock could be rewritten to store the argument using jest.fn(fn => { callback = fn; });but the same error happens when using foo.addListener.mockClear()which cannot be reworked the same way.
在这个简单的代码中，可以重写模拟来存储参数 usingjest.fn(fn => { callback = fn; });但在 using 时会发生相同的错误，foo.addListener.mockClear()而不能以相同的方式重新编写。
So how can I get rid of the error, preferably without losing type-safety?
那么我怎样才能摆脱错误，最好在不失去类型安全的情况下呢？
回答by Brian Adams
You can use jest.spyOnin combination with functions like mockImplementationto mock a function while preserving type safety in TypeScript:
您可以jest.spyOn与类似mockImplementation模拟函数的函数结合使用，同时在 TypeScript 中保留类型安全性：
class Foo {
addListener = (callback: () => number) => { }
func = () => {
this.addListener(() => 1);
}
}
test('working', () => {
const foo = new Foo();
const mockAddListener = jest.spyOn(foo, 'addListener'); // spy on foo.addListener
mockAddListener.mockImplementation(() => { }); // replace the implementation if desired
foo.func(); // will call addListener with a callback
const callback = mockAddListener.mock.calls[0][0];
expect(callback()).toEqual(1); // SUCCESS
});
回答by gztomas
For anyone getting here, a bit better than casting to anymight be casting as jest.Mock
对于到达这里的任何人来说，比投射到any可能会投射为 jest.Mock 好一点
const callback = (foo.addListener as jest.Mock).mock.calls[0][0];
