我想用Jest模拟一个函数,但只有在使用特定参数调用它时,例如:
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)
Ruby的RSpec库中实现了类似的功能:
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)
我在测试中想要实现的是更好的解耦,假设我想测试一个依赖于的函数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以下方式实现:
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");
但如果我们有一些糖功能来简化它会很好.
听起来合理吗？我们在Jest中已经有这个功能吗？
感谢您的反馈意见.
我找到了我的同事最近写的这个图书馆: 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!');
这是图书馆:https://github.com/timkindberg/jest-when
没有办法在Jest中做到这一点.你可以使用sinons存根.来自文档:
stub.withArgs(arg1 [,arg2,...]);
仅为提供的参数存储方法.这对于在断言中更具表现力很有用,您可以使用相同的调用访问间谍.创建一个可以不同方式响应不同参数的存根也很有用.
"test should stub method differently based on arguments": function () {
var callback = sinon.stub();
callback.withArgs(42).returns(1);
callback.withArgs(1).throws("TypeError");
callback(); // No return value, no exception
callback(42); // Returns 1
callback(1); // Throws TypeError
}
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