I would like to test that the following function performs as expected:
function throwNextTick(error) {
process.nextTick(function () {
throw error;
});
}
Here is my attempt:
describe("throwNextTick", function () {
it("works as expected", function (next) {
var error = new Error("boo!");
var recordedError = null;
process.once("uncaughtException", function (error) {
recordedError = error;
});
throwNextTick(error);
process.nextTick(function () {
recordedError.should.be(error);
next();
});
});
});
But mocha seems to want to keep any errors to itself, and fail my test when it gets them:
C:\Users\ddenicola\Programming (Synced)\pubit>mocha test/basicTest.js
throwNextTick
0) works as expected
? 1 of 1 tests failed:
1) throwNextTick works as expected:
Error: boo!
at Test.fn (C:\Users\ddenicola\Programming (Synced)\pubit\test\basicTest.js:11:21)
at Test.run (C:\Users\ddenicola\AppData\Roaming\npm\node_modules\mocha\lib\runnable.js:144:15)
at Runner.runTest (C:\Users\ddenicola\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:271:10)
at C:\Users\ddenicola\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:315:12
at next (C:\Users\ddenicola\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:199:14)
at C:\Users\ddenicola\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:208:7
at next (C:\Users\ddenicola\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:157:23)
at Array.0 (C:\Users\ddenicola\AppData\Roaming\npm\node_modules\mocha\lib\runner.js:176:5)
at EventEmitter._tickCallback (node.js:192:40)
Any ideas?
A pending test in many test framework is test that the runner decided to not run. Sometime it's because the test is flagged to be skipped. Sometime because the test is a just a placeholder for a TODO. For Mocha, the documentation says that a pending test is a test without any callback.
Introduction to Unit Testing with Mocha and Chai Mocha is a widely used JavaScript test framework running on NodeJS and browsers. It supports asynchronous testing running the tests serially, allowing for more flexible and accurate reporting.
Update: Courtesy of casey-foster in a comment below:
As of node v6.0.0 you can use
process.prependOnceListener('uncaughtException', ...)
to do this much more succinctly.
Old answer:
The secret lies in process.listeners('uncaughtException'):
http://nodejs.org/docs/latest/api/events.html#emitter.listeners
Simply remove the mocha listener, add your own, then reattach the mocha listener.
See below:
var assert = require('assert')
function throwNextTick(error) {
process.nextTick(function () {
throw error
})
}
describe("throwNextTick", function () {
it("works as expected", function (next) {
var error = new Error("boo!")
var recordedError = null
var originalException = process.listeners('uncaughtException').pop()
//Needed in node 0.10.5+
process.removeListener('uncaughtException', originalException);
process.once("uncaughtException", function (error) {
recordedError = error
})
throwNextTick(error);
process.nextTick(function () {
process.listeners('uncaughtException').push(originalException)
assert.equal(recordedError, error)
next()
})
})
})
If your async code is executed within a domain - and that is often the case - you need to change the error listener on the domain instead of the process.
For that you can use:
it('should produce an unhandled exception', function (done) {
// Remove Mocha's error listener
var originalErrorListeners = process.domain.listeners('error');
process.domain.removeAllListeners('error');
// Add your own error listener to check for unhandled exceptions
process.domain.on('error', function () {
// Add the original error listeners again
process.domain.removeAllListeners('error');
for ( var i = 0; i < originalErrorListeners.length; i+=1 ) {
process.domain.on('error', originalErrorListeners[i]);
}
// For the sake of simplicity we are done after catching the unhandled exception
done();
});
// This would be your async application code you expect to throw an exception
setTimeout(function () {
throw new Error();
});
});
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