问题描述
class TestObject {
constructor(value) {
if (value === null || value === undefined) {
throw new Error('Expect a value!');
}
}
}
describe('test the constructor', () => {
test('it works', () => {
expect(() => {
new TestObject();
}).toThrow();
});
test('not work', () => {
expect(new TestObject()).toThrow();
});
});
这里有2个测试用例，一个有效，而另一个无效.
2 Test cases here, one works and the other not.
not work的失败消息如下:
期望值！
at new TestObject (tests/client/utils/aaa.test.js:4:11)
at Object.<anonymous> (tests/client/utils/aaa.test.js:17:12)
at Promise (<anonymous>)
at <anonymous>
at process._tickCallback (internal/process/next_tick.js:188:7)
为什么我需要在函数调用中包装该调用，而当该函数仅返回一个简单值甚至是一个承诺时，我们就不需要包装，我们可以使用async/await在expect()中进行检查而不是在expect()中创建一个函数.
Why do I need to wrap that call in a function call, we don't need to wrap when the function just return a plain value, or even a promise, we can use async/await to check that in expect() rather than create a function inside expect().
这里发生了什么?
推荐答案
此处
expect(new TestObject()).toThrow();
根据运算符优先级.当new TestObject()抛出时，其他任何都无所谓.
new TestObject() is evaluated first, then expect(...), then ...toThrow(), in accordance with operator precedence. When new TestObject() throws, anything else doesn't matter.
这就是为什么toThrow需要一个应该抛出的函数的原因:
This is why toThrow expects a function that is supposed to throw:
expect(() => {
new TestObject();
}).toThrow();
这样，在调用它时可以在内部用try..catch包裹它.
This way it can be wrapped with try..catch internally when being called.
在Jasmine toThrow和Chai to.throw断言中也是如此.
It works similarly in Jasmine toThrow and Chai to.throw assertions as well.
这篇关于当直接在构造函数中创建ES6类的实例时，为什么Jest的toThrow无法正常工作?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！