有没有办法让Chai使用异步Mocha测试？
有没有办法让Chai使用异步Mocha测试？
提问于 2012-06-28 06:43:58
我正在使用Browser Runner在Mocha中运行一些异步测试，并尝试使用Chai的expect风格断言：
window.expect = chai.expect;
describe('my test', function() {
it('should do something', function (done) {
setTimeout(function () {
expect(true).to.equal(false);
}, 100);
}
}这并没有给出正常的失败断言消息，相反，我得到：
Error: the string "Uncaught AssertionError: expected true to equal false" was thrown, throw an Error :)
at Runner.fail (http://localhost:8000/tests/integration/mocha/vendor/mocha.js:3475:11)
at Runner.uncaught (http://localhost:8000/tests/integration/mocha/vendor/mocha.js:3748:8)
at uncaught (http://localhost:8000/tests/integration/mocha/vendor/mocha.js:3778:10)所以很明显它捕捉到了错误，只是没有正确地显示出来。你知道该怎么做吗？我想我可以用一个错误对象来调用"done“，但这样我就失去了像Chai这样的东西的优雅，它变得非常笨拙……
回答 13
Stack Overflow用户
回答已采纳
发布于 2013-03-05 02:07:24
异步测试在失败的expect()操作上生成一个异常，it()无法捕获该异常，因为该异常被抛出在it()的作用域之外。
显示的捕获异常是使用node下的process.on('uncaughtException')或浏览器中的window.onerror()捕获的。
要解决此问题，您需要在setTimeout()调用的异步函数中捕获异常，以便以异常作为第一个参数调用done()。您还需要调用不带参数的done()来表示成功，否则mocha将报告一个超时错误，因为您的测试函数永远不会发出已完成的信号：
window.expect = chai.expect;
describe( 'my test', function() {
it( 'should do something', function ( done ) {
// done() is provided by it() to indicate asynchronous completion
// call done() with no parameter to indicate that it() is done() and successful
// or with an error to indicate that it() failed
setTimeout( function () {
// Called from the event loop, not it()
// So only the event loop could capture uncaught exceptions from here
try {
expect( true ).to.equal( false );
done(); // success: call done with no parameter to indicate that it() is done()
} catch( e ) {
done( e ); // failure: call done with an error Object to indicate that it() failed
}
}, 100 );
// returns immediately after setting timeout
// so it() can no longer catch exception happening asynchronously
}
}在所有测试用例上这样做既烦人又不干练，因此您可能希望提供一个函数来为您完成此操作。让我们将此函数称为check()
function check( done, f ) {
try {
f();
done();
} catch( e ) {
done( e );
}
}使用check()，您现在可以重写异步测试，如下所示：
window.expect = chai.expect;
describe( 'my test', function() {
it( 'should do something', function( done ) {
setTimeout( function () {
check( done, function() {
expect( true ).to.equal( false );
} );
}, 100 );
}
}Stack Overflow用户
发布于 2015-12-19 11:33:53
以下是我对ES6/ES2015 promises和ES7/ES2016 async/await的通过测试。希望这篇文章能为任何研究这个话题的人提供一个很好的更新答案：
import { expect } from 'chai'
describe('Mocha', () => {
it('works synchronously', () => {
expect(true).to.equal(true)
})
it('works ansyncronously', done => {
setTimeout(() => {
expect(true).to.equal(true)
done()
}, 4)
})
it('throws errors synchronously', () => {
return true
throw new Error('it works')
})
it('throws errors ansyncronously', done => {
setTimeout(() => {
return done()
done(new Error('it works'))
}, 4)
})
it('uses promises', () => {
var testPromise = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('Hello')
}, 4)
})
testPromise.then(result => {
expect(result).to.equal('Hello')
}, reason => {
throw new Error(reason)
})
})
it('uses es7 async/await', async (done) => {
const testPromise = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('Hello')
}, 4)
})
try {
const result = await testPromise
expect(result).to.equal('Hello')
done()
} catch(err) {
done(err)
}
})
/*
* Higher-order function for use with async/await (last test)
*/
const mochaAsync = fn => {
return async (done) => {
try {
await fn()
done()
} catch (err) {
done(err)
}
}
}
it('uses a higher order function wrap around async', mochaAsync(async () => {
const testPromise = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('Hello')
}, 4)
})
expect(await testPromise).to.equal('Hello')
}))
})Stack Overflow用户
发布于 2014-02-10 23:22:35
如果你喜欢promised，试试Chai as Promised + Q，它允许这样的东西：
doSomethingAsync().should.eventually.equal("foo").notify(done);页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/11235815
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