我正在编写一堆 mocha 测试,我想测试是否发出了特定事件。目前,我正在这样做:
it('should emit an some_event', function(done){
myObj.on('some_event',function(){
assert(true);
done();
});
});
但是,如果该事件从未发出,它会使测试套件崩溃,而不是使该测试失败。
测试这个的最佳方法是什么?
我正在编写一堆 mocha 测试,我想测试是否发出了特定事件。目前,我正在这样做:
it('should emit an some_event', function(done){
myObj.on('some_event',function(){
assert(true);
done();
});
});
但是,如果该事件从未发出,它会使测试套件崩溃,而不是使该测试失败。
测试这个的最佳方法是什么?
If you can guarantee that the event should fire within a certain amount of time, then simply set a timeout.
it('should emit an some_event', function(done){
this.timeout(1000); //timeout with an error if done() isn't called within one second
myObj.on('some_event',function(){
// perform any other assertions you want here
done();
});
// execute some code which should trigger 'some_event' on myObj
});
If you can't guarantee when the event will fire, then it might not be a good candidate for unit testing.
9月30日编辑:
我看到我的答案被接受为正确答案,但 Bret Copeland 的技术(见下面的答案)更好,因为它在测试成功时更快,这将是大多数情况下作为测试套件的一部分运行测试的情况.
Bret Copeland 的技术是正确的。你也可以做一些不同的事情:
it('should emit an some_event', function(done){
var eventFired = false
setTimeout(function () {
assert(eventFired, 'Event did not fire in 1000 ms.');
done();
}, 1000); //timeout with an error in one second
myObj.on('some_event',function(){
eventFired = true
});
// do something that should trigger the event
});
这可以在Sinon.js的帮助下缩短一点。
it('should emit an some_event', function(done){
var eventSpy = sinon.spy()
setTimeout(function () {
assert(eventSpy.called, 'Event did not fire in 1000ms.');
assert(eventSpy.calledOnce, 'Event fired more than once');
done();
}, 1000); //timeout with an error in one second
myObj.on('some_event',eventSpy);
// do something that should trigger the event
});
在这里,我们不仅要检查是否触发了事件,还要检查是否在超时期间仅触发了一次 if 事件。
Sinon 还支持calledWith
andcalledOn
来检查使用了哪些参数和函数上下文。
请注意,如果您希望事件与触发事件的操作同步触发(中间没有异步调用),那么您可以将超时设置为零。1000 ms 的超时仅在您执行异步调用时才需要,这需要很长时间才能完成。很可能不是这样。
实际上,当事件保证与导致它的操作同步触发时,您可以将代码简化为
it('should emit an some_event', function() {
eventSpy = sinon.spy()
myObj.on('some_event',eventSpy);
// do something that should trigger the event
assert(eventSpy.called, 'Event did not fire.');
assert(eventSpy.calledOnce, 'Event fired more than once');
});
否则,Bret Copeland 的技术在“成功”情况下(希望是常见情况)总是更快,因为它能够done
在事件被触发时立即调用。
这种方法确保了最短的等待时间,但套件超时设置的最大机会,并且非常干净。
it('should emit an some_event', function(done){
myObj.on('some_event', done);
});
也可以将它用于 CPS 风格的功能......
it('should call back when done', function(done){
myAsyncFunction(options, done);
});
这个想法也可以扩展到检查更多细节 - 例如参数和this
- 通过放置一个包装器 arround done
。例如,多亏了这个答案,我可以做...
it('asynchronously emits finish after logging is complete', function(done){
const EE = require('events');
const testEmitter = new EE();
var cb = sinon.spy(completed);
process.nextTick(() => testEmitter.emit('finish'));
testEmitter.on('finish', cb.bind(null));
process.nextTick(() => testEmitter.emit('finish'));
function completed() {
if(cb.callCount < 2)
return;
expect(cb).to.have.been.calledTwice;
expect(cb).to.have.been.calledOn(null);
expect(cb).to.have.been.calledWithExactly();
done()
}
});
坚持:
this.timeout(<time ms>);
在您的 it 声明的顶部:
it('should emit an some_event', function(done){
this.timeout(1000);
myObj.on('some_event',function(){
assert(true);
done();
});`enter code here`
});
在这里聚会迟到了,但我正面临这个问题,并想出了另一个解决方案。Bret 接受的答案是一个很好的答案,但我发现它在运行我的完整 mocha 测试套件时造成了严重破坏,抛出了错误done() called multiple times
,我最终放弃了尝试进行故障排除。Meryl 的回答让我走上了我自己的解决方案的道路,该解决方案也使用sinon
,但不需要使用超时。通过简单地存根emit()
方法,您可以测试它是否被调用并验证它的参数。这假设您的对象继承自 Node 的 EventEmitter 类。在您的情况下,方法的名称emit
可能会有所不同。
var sinon = require('sinon');
// ...
describe("#someMethod", function(){
it("should emit `some_event`", function(done){
var myObj = new MyObj({/* some params */})
// This assumes your object inherits from Node's EventEmitter
// The name of your `emit` method may be different, eg `trigger`
var eventStub = sinon.stub(myObj, 'emit')
myObj.someMethod();
eventStub.calledWith("some_event").should.eql(true);
eventStub.restore();
done();
})
})
我建议使用once()
更简单的解决方案,特别是如果您喜欢 async/await 风格:
const once = require('events').once
// OR import { once } from 'events'
it('should emit an some_event', async function() {
this.timeout(1000); //timeout with an error if await waits more than 1 sec
p = once(myObj, 'some_event')
// execute some code which should trigger 'some_event' on myObj
await p
});
如果您需要检查值:
[obj] = await p
assert.equal(obj.a, 'a')
最后,如果您使用的是打字稿,以下帮助程序可能会很方便:
// Wait for event and return first data item
async function onceTyped<T>(event: string): Promise<T> {
return <T>(await once(myObj, event))[0]
}
像这样使用:
const p = onceTyped<SomeEvent>(myObj, 'some_event')
// execute some code which should trigger 'some_event' on myObj
const someEvent = await p // someEvent has type SomeEvent
assert.equal(someEvent.a, 'a')
代替 sinon.timers更好的解决方案是使用es6 - Promises:
//Simple EventEmitter
let emitEvent = ( eventType, callback ) => callback( eventType )
//Test case
it('Try to test ASYNC event emitter', () => {
let mySpy = sinon.spy() //callback
return expect( new Promise( resolve => {
//event happends in 300 ms
setTimeout( () => { emitEvent('Event is fired!', (...args) => resolve( mySpy(...args) )) }, 300 ) //call wrapped callback
} )
.then( () => mySpy.args )).to.eventually.be.deep.equal([['Event is fired!']]) //ok
})
如您所见,关键是用 resolve: (... args) => resolve (mySpy (... args))包装回调。
因此,PROMIS new Promise().then()只有在被调用回调之后才会被解析。
但是一旦回调被调用,你就可以测试你对他的期望。
优点:
I do it by wrapping the event in a Promise:
// this function is declared outside all my tests, as a helper
const waitForEvent = (asynFunc) => {
return new Promise((resolve, reject) => {
asyncFunc.on('completed', (result) => {
resolve(result);
}
asyncFunc.on('error', (err) => {
reject(err);
}
});
});
it('should do something', async function() {
this.timeout(10000); // in case of long running process
try {
const val = someAsyncFunc();
await waitForEvent(someAsyncFunc);
assert.ok(val)
} catch (e) {
throw e;
}
}