我可以使用Jest模拟具有特定参数的函数吗? [英] Can I mock functions with specific arguments using Jest?
问题描述
我想用Jest来模拟一个函数,但仅当使用特定参数调用该函数时,例如:
I would like to mock a function with Jest, but only if it is called with specific arguments, for example:
function sum(x, y) {
return x + y;
}
// mock sum(1, 1) to return 4
sum(1, 1) // returns 4 (mocked)
sum(1, 2) // returns 3 (not mocked)
在Ruby的RSpec库中实现了类似的功能:
There is a similar feature implemented in the Ruby's RSpec library:
class Math
def self.sum(x, y)
return x + y
end
end
allow(Math).to receive(:sum).with(1, 1).and_return(4)
Math.sum(1, 1) # returns 4 (mocked)
Math.sum(1, 2) # returns 3 (not mocked)
我想在测试中实现的是更好的去耦,比如说我要测试依赖于sum
的函数:
What I'm trying to achieve in my tests is a better decoupling, let's say I want to test a function that relies on sum
:
function sum2(x) {
return sum(x, 2);
}
// I don't want to depend on the sum implementation in my tests,
// so I would like to mock sum(1, 2) to be "anything I want",
// and so be able to test:
expect(sum2(1)).toBe("anything I want");
// If this test passes, I've the guarantee that sum2(x) is returning
// sum(x, 2), but I don't have to know what sum(x, 2) should return
我知道有一种方法可以通过执行以下操作来实现:
I know that there is a way to implement this by doing something like:
sum = jest.fn(function (x, y) {
if (x === 1 && y === 2) {
return "anything I want";
} else {
return sum(x, y);
}
});
expect(sum2(1)).toBe("anything I want");
但是如果我们有一些糖功能来简化它,那就太好了.
But it would be nice if we had some sugar function to simplify it.
听起来合理吗?我们在Jest中已经拥有此功能吗?
Does it sounds reasonable? Do we already have this feature in Jest?
感谢您的反馈.
推荐答案
我找到了我的一位同事最近写的这个库:jest-when
I found this library that a colleague of mine wrote recently: jest-when
import { when } from 'jest-when';
const fn = jest.fn();
when(fn).calledWith(1).mockReturnValue('yay!');
const result = fn(1);
expect(result).toEqual('yay!');
这里是图书馆: https://github.com/timkindberg/jest-when
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