我正在尝试测试一些邮件代码的失败模式,在最低级别可能会抛出一个错误。测试和抛出函数之间的所有层都是异步的,并在它们下面的函数上使用await。在顶层(同样在异步函数中,我有一个try catch块。但是,在错误传播到此级别之前,节点正在引发未处理的promise异常。
我的测试代码如下所示
beforeEach(function() {
//set default values - tests can change them
this.reasons = '';
this.reschedules = 0;
this.params.cid = 35124;
this.startTest = async () => {
/* this.confirmation is an async function under test,
this.mailer is a mock mailer with an async "send" method
which will throw an error in the correct test */
const doner = this.confirmation(this.mailer);
// ..other actions related to mocking database access made by confirmation
await doner;
return this.mailer.maildata; //provide info on parameters passed to this.mailer
};
});
it('Failure to send is reported', async function() {
this.mailer.sendResolve = false; //tell mock mailer to fail send request
try {
await this.startTest();
expect(true).to.be.false;
} catch(err) {
expect(err).to.be.instanceOf(Error);
}
});
模拟邮件程序有点像这样
class Mailer {
constructor(user,params){
...
}
...
async send(subject, to, cc, bcc) {
this.maildata.subject = subject;
if (to !== undefined) this.maildata.to = to;
if (cc !== undefined) this.maildata.cc = cc;
if (bcc !== undefined) this.maildata.bcc = bcc;
if (!this.sendResolve) throw new Error('Test Error');
}
...
}
以及测试代码的摘要
module.exports = async function(mailer) {
//get confirm data from database
const cData = await confirm(mailer.params.cid, mailer.db);
if (cData.count > 0) {
// ... format the email message and build it into maildata
await mailer.send(
subject,
emailAddress,
null,
process.env.PAS_MAIL_FROM,
{
pid:cData.pid,
type: 'confirmation',
extra: `Calendar ID ${mailer.params.cid} with procedure ${cData.procedure}`
}
);
debug('message sent, update the database');
await mailer.db.exec(async connection => {
...
});
debug('success');
} else {
debug('invalid calendarid');
throw new Error('Invalid Calendar ID');
}
};
可以看出,从异步发送
函数的调用路径将堆栈抛回try{}catch(){}
都是异步函数。但是当我运行这个测试节点时,会输出一个未处理的promise拒绝。
我尝试过使用可视化工作室代码调试器来单步执行此步骤,我有点迷失在包装异步函数以将它们转换为promise提供者的机器中。据我所知,一层错误被正确处理,然后在下一层失败。
这是不是意味着每个异步函数都必须有一个try catch块来捕捉并重新抛出任何错误?我找不到任何解释说我必须这么做。
回答你的问题:
这是否意味着每个异步函数都必须有一个try catch块来捕获和重新抛出任何错误?
错误通过<code>发出,并等待-ed调用,如您所期望的:
const assert = require('assert');
const outer = async () => {
await middle();
}
const middle = async () => {
await inner();
}
const inner = async () => {
throw new Error('something bad happened');
}
it('should catch the error', async () => {
let errorMessage;
try {
await outer();
}
catch (err) {
errorMessage = err.message;
}
assert(errorMessage === 'something bad happened'); // Success!
});
...所以不,你不需要在每一层都有一个< code>try / catch块。
追踪未处理的promise
拒绝
我看不到wait
链在您的示例代码中的确切位置可能会被破坏,但为了帮助跟踪未处理的Promise
拒绝,您可以为unhandledReject
事件添加一个进程处理程序,并查看记录的Promise
以查看拒绝的开始位置,并从那里通过调用堆栈向后跟踪:
const assert = require('assert');
const outer = async () => {
await middle();
}
const middle = async () => {
inner(); // <= this will cause an Unhandled Rejection
}
const inner = async () => {
throw new Error('something bad happened');
}
it('should catch the error', async () => {
let errorMessage;
try {
await outer();
}
catch (err) {
errorMessage = err.message;
}
assert(errorMessage === undefined); // Success! (broken await chain)
})
process.on('unhandledRejection', (reason, p) => {
console.log('Unhandled Rejection at:', p);
console.log('reason:', reason);
});
…在这种情况下记录:
Unhandled Rejection at: Promise {
<rejected> Error: something bad happened
at inner (.../code.test.js:12:9)
at inner (.../code.test.js:8:3)
at middle (.../code.test.js:4:9) // <= this is the broken link
at Context.outer (.../code.test.js:18:11)
at callFn (...\node_modules\mocha\lib\runnable.js:387:21)
...
…这将我们指向内部
中抛出的错误
,通过跟踪链,我们发现中间
是断开的链接。