calling kriskowal type promise function in Mocha's before and after function

Question

Hi folks so I'm writing Mocha test to test my Node.js server. The test just needs to check if a json file IO utility I wrote can correctly write files. One of the issues is that I'm not sure how I properly call an async function(which returns a kriskowal/q type promise) in the before function. I need to wait for the async function in the before section to finish before running the test case.

According to https://mochajs.org/#asynchronous-code, the before function needs to take a "done" callback for it to be waited until finish. But since my function returns a promise can I simply do the following to utilize the done function : ?

describe("test create/read/delete json file", function () {
    before(function (done) {
        fileHelper.writeJsonFile(mailTypeFile, json, {spaces: 2}).then(function () {
            done();
        }).catch(function (error) {
            done(error);
        })
    });

    after(function (done) {
        fileHelper.deleteFile(mailTypeFile).then(function () {
            done();
        }).catch(function (error) {
            done(error);
        })
    });

    it('should create mailtype', function (done) {
        fileHelper.readJsonFile(mailTypeFile).then(function (data) {
            expect(data).to.have.property('required');
            expect(data).to.have.property('properties');
            done();
        }).catch(function (error) {
            done(error);
        })
    })
});

So I call done() if the promise resolves and done(err) if the promise rejects. Is it guaranteed to wait for the before() to finish ?

Louis · Accepted Answer · 2016-07-18 23:20:15Z

1

Since your functions return promises, you can just return the promise. Mocha will wait for the promise to be resolved or rejected before moving to the next thing. Do not declare done in the parameters of your anonymous functions you pass to it, before, after and do not call it.

answered Jul 18, 2016 at 23:20

Louis

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2 Comments

Calvin Hu Over a year ago

But since my promise is a Q promise which follows a then()..catch()..done() format which is different from other common promise syntax, is it still allow to return such a promise inside before?

Louis Over a year ago

Mocha is not going to call the promise's .done() for you. What this means is that if there's an error in Mocha's rejection handler, then the error won't be caught. However, this would mean that Mocha is buggy. I don't write my tests with the assumption that Mocha is not running correctly and I don't think it is wise to do so because there's really no end to the number of ways in which Mocha could fail to run correctly.

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