[英]Jest - how to mock a method within a function
I have an ES6 class A, that I need to test, the only thing I want to change is the implementation of one method, and all the other things to remain as they are. 我有一个ES6类A,需要测试,我唯一想更改的就是一种方法的实现,而其他所有东西则保持不变。
First, I wanted manually to create a mock class like "myMock extends A" where I would change that method and use it for tests, but there were some problems. 首先,我想手动创建一个类似“ myMock extended A”的模拟类,在该类中我将更改该方法并将其用于测试,但是存在一些问题。
Anyway, is there another way with jest to specify replacement of a specific method within a class? 无论如何,还有什么用笑话来指定类中特定方法的替换吗?
What I tried to do now is following: 我现在尝试做的是:
jest.mock("../myclass", () => {
return jest.fn().mockImplementation(() => {
return {
loadPopularItems: jest.fn(() => new Promise((resolve): void =>
resolve()))
};
});
});
This now gives me an error that myclass is not a constructor: 现在这给了我myclass不是构造函数的错误:
TypeError: myclass`.default is not a constructor TypeError:myclass`.default不是构造函数
All I want to do is remove some async method from there, that makes HTTP requests. 我要做的就是从那里删除一些异步方法,该方法发出HTTP请求。
You can stub out the method on the prototype in your test: 您可以在测试中将方法存入原型:
A.prototype.loadPopularItems = jest.fn()
Or you can use jest.spyOn
to allow for easily resetting mocks: 或者,您可以使用jest.spyOn
来轻松重置jest.spyOn
:
jest.spyOn(A.prototype, "loadPopularItems");
jest.restoreAllMocks(); // avoids having to manually track mocks
Better yet, have your class accept whatever object/function makes HTTP requests as a constructor argument: 更好的是,让您的类接受构成HTTP请求的任何对象/函数作为构造函数参数:
class A {
constructor(http) {
this.http = http;
}
loadPopularItems() {
return this.http.fetchSomething();
}
}
Then in your tests you can just pass a fake implementation: 然后在测试中,您可以通过一个伪造的实现:
const fakeHttp = {
fetchSomething: jest.fn()
};
const instance = new A(fakeHttp);
This is generally the preferable over stubbing out methods. 通常,这比结束方法更可取。
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