Mocha: --order option for random test order?

meh, pretty easy to avoid cross-test dependencies without help of tooling

While it is easy to avoid cross-test dependencies without help of tooling, it is also easy to add such a dependency in a test suite without noticing. A bug in the test suite usually translates to a bug in a tested system. These bugs are hard to trace, as the code is supposedly test-covered.

Testing for absence of cross-test dependencies is impossible without tooling.

@visionmedia, please reconsider.

+1 @yanovich. I would use a random order option which outputs a seed number. This would be very useful in a CI environment.

@visionmedia, mongoose models provide an easy example of cross-test dependencies. mongoose.model 'User', UserSchema adds a model onto the array of mongoose.models. So it's possible to create a file which relies on the user model being loaded in mongoose.models. Take Comment.find().populate('_user').exec(cb) as an example. If the user test runs before the comment test, this will execute fine, because presumably require('./models/user') (or something), has loaded the User model into mongoose.models. But if the comment test executes before the user test you'll get this error Schema hasn't been registered for model "User". This could happen in production when the comment api runs before the user api and the comment file didn't know it had a cross file dependency.

It is possible to still have the production problem with the test working if the test file has require('./models/user') (or whatever) and that loads the user into mongoose.models. However having a random order would be one more useful tool to discover potential problems like this.

I hope articulated that well. Looking forward to hearing your thoughts.

sorry, I think it's major overkill, mocha is bloated enough as-is. If there was a lot more interest then perhaps it would be worth the maintenance burden.

Thanks for thinking about it.

Like most things in code, it's easy for people who know to avoid doing this intentionally. It's harder to avoid doing it unintentionally. And if you don't know it's even a problem (i.e mixed experience teams) it's downright likely to happen :)

Seems like quite a few ppl are interested in it (and lots think it's one of the best features of minitest). If it'd get merged I'm happy to implement.

+1 interested.

Would be nice to have! I found my tests to fails by renaming file names, ugh.

+1 this is important

:+1:

:+1:

+1 This is a pretty big deficiency.

rspec semantics are pretty solid: you can pass an order seed, or it can pick it at random. If it picks the seed at random, it prints it out, so it's easy to reproduce.

It's often not that easy to avoid cross-test dependencies. Sometimes due to unforeseen global interactions, sometimes out of convenience. I suspect more than 50% of projects that use mocha would see test failures if the order was randomized. Here's a couple examples that appear to rely on the order of the test execution:

https://github.com/visionmedia/mocha/blob/master/test/hook.async.js#L95
https://github.com/visionmedia/superagent/blob/master/test/node/not-modified.js#L31

These two are listed as exemplar test suites on http://visionmedia.github.io/mocha/ and I didn't spend much time looking for issues.

I'll reopen this. I think it'd be helpful. While there are ways to determine cross-test deps w/o tooling, if we can automate that, it'd save people time.

After toying with this a bit, it appears non-trivial due to the hierarchical nature of Suites. Tests are run by recursing into Suites. To run _Tests_ randomly, we'd have to enumerate them, randomize them, then work backwards.

This would cause before() and after() Hooks to be somewhat meaningless as they would get executed _n_ times per _n_ tests in a Suite (or rather, in the _worst_ case, but only if we're careful), as we continually change contexts. Sounds like it'll incur a performance penalty.

Using random seeds and reporting auto-generated seeds seems trivial, however, reporters may need to know about this information, so that requires implementation(s) in the reporters.

Of course, I'm assuming what I've described here is what's being asked for. A feature like this needs a specification.

Other options include "randomize Suites" or "randomize tests within Suites" or some combination of the two. Practically speaking, this means that once you're in a describe() block _A_, you cannot execute tests in any parent or sibling describe() block _B_ until all of the tests in _A_ have been run (which looks to be a much more straightforward implementation, and won't cause hinkiness with before()/after()).

What I am (and I think others are) asking for is the simplest of the options:

• randomize the tests at the lowest level: within a single describe block; shuffle "it" statements.
• randomize the order of top level suites (or randomize the order of files that get loaded)

I don't think there's much value in shuffling things at the intermediate levels.

Certainly a hack, but works for the lowest level https://github.com/syrnick/mocha/compare/random_order?expand=1&w=0

mocha - fail
connect - pass
superagent - fail
express - pass** 
websocket.io - pass (can't tell for sure)

** I got 2 intermittent failures out of 100 runs of the whole test suite either way.

OK, that's certainly eaiser to implement!

I was looking at the seedrandom lib for this; use the pass option.

Would accept PR.

I'll likely clean up that code and adjust the test suite over the next few days. Is underscore too heavy of a dependency for this? I could likely use something light like this: http://stackoverflow.com/questions/6274339/how-can-i-shuffle-an-array-in-javascript.

@boneskull I support your decision to reopen this. :+1:

Other options include "randomize Suites" or "randomize tests within Suites" or some combination of the two.

Seems more than good enough for me. No need to recurse all the way down, enumerate and shuffle.

Great to hear this is going in.

I wonder if rspec has handled the recursive shuffle? Might be worth looking
at their code?

On Tuesday, 26 August 2014, Joshua Appelman [email protected]
wrote:

@boneskull https://github.com/boneskull I support your decision to
reopen this. [image: :+1:]

Other options include "randomize Suites" or "randomize tests within
Suites" or some combination of the two.

Seems more than good enough for me. No need to recurse all the way down,
enumerate and shuffle.

—
Reply to this email directly or view it on GitHub
https://github.com/visionmedia/mocha/issues/902#issuecomment-53482124.

@syrnick I would not want to accept a PR with such a large dependency, and instead use seedrandom. Without it, I'm not sure how you're going to support seeding. seedrandom allows you to specify a seed or not, and if you don't, it will return a seed to you. Then we could display it to the user and allow them to specify it, a la RSpec.

@syrnick Mind you that if you do generate seeds, they may not be "displayable" without passing them off to reporters. I'm not very familiar with the reporting architecture, so I couldn't tell you for sure, or what to do...

+1

I haven't looked at the implementation, but +1 to randomly-ordered test execution by default being super important.

@syrnick Please let me know if you intend to do this, thanks.

I'm happy to do that, but I don't have an immediate ETA.

:+1:, you guys still need help with a PR?

Indeed, no one seems to have started working on this.

First, it looks like a Fisher-Yates shuffle would do the job here.

Second, I'd rather have --order random, --order random-suites, and --order default as the three arguments, with an optional :<seed>.

+1. Just found a bug that would've shown up a long time ago if tests were randomized. Similar to how RSpec supports it.

Here's some code that illustrates the usefulness of random test ordering. While there are simpler examples, this is one I just encountered during a TDD demo. If you reverse the order of the tests, the first test always fails.

game.js:

var express = require('express');
app = exports.app = express();

var sum = 0;

app.post('/bowl/:pins', function(req,res) {
    var score = parseInt(req.params.pins);
    console.log('Bowled ' + score);
    sum += parseInt(req.params.pins);
});

app.get('/score', function(req,res) {
    console.log('Sum: ' + sum);
    res.send(sum + '');
});

app.listen(process.env.PORT || 3000);

test\gameTest.js:

var request = require('supertest'),
    should = require('should'),
    game = require('../game.js').app;

describe('a game of bowling', function() {
    describe('a gutter game', function() {
        it('should score 0', function(done){
            request(game).get('/score').expect(200, '0', done);
        });
    });

    describe('a single pin game', function() {
        it('should score 20', function(done){
            for(var i = 0; i < 20; i++) {
                request(game).post('/bowl/1').expect(200, done);
            }
            request(game).get('/score').expect(200, '20', done); 
        });
    });
});

I would love to have this.

:+1:

Once you get a few globals involved (this is Javascript, remember), start stubbing out server calls, and inserting/removing things from the DOM in your tests, it is _very_ easy to add order-dependency. Randomizing the test order would help discover these earlier rather than later.
:+1:

:+1:

:+1:

+1

Random order by default, with optional seed to recreate ordering, would be a great feature to have.

+1 to have it, my tests sometime fail when run in random order...

In the mean time, unix to the rescue (Unfortunately, random seed no supported):

mocha `ls -1 test/*.js | sort --random-sort `

Was googling for what order mocha runs tests in and found this. In absence of randomization, what is the default run order? Is it always the order in which the tests appear physically in the file?

:+1:

@danielabar yeah they'll be in-order they appear in the file.

@NicolasJacob well, random seed is actually possible to some extent, btw. :)

$ seq 10 | shuf --random-source=<(yes 2883)
1
7
3
4
6
2
10
5
9
8

https://github.com/bahmutov/rocha works for this.

@boneskull whilst this is an old issue, is the PR Please label still valid? If so I'll get something contributed in the next day or so.

I think in the pursuit of eventually trying to keep the mocha core minimal, the team might be hesitant in introducing many new features. The next major release of mocha has the goal of having a pluggable interface.

Might I suggest just using https://github.com/bahmutov/rocha if it works?

Awesome sauce

What do you mean by pluggable interface? Will it be possible to introduce a randomized testing order via this interface?

+1 for the feature request

@sulabhjain, previous and following supporters, please use the +1 reaction instead.

Progress in this branch.

+1 for this feature

This is really one the most critical features for a testing framework to help keep tests independent. Every major JVM test framework has this basic feature.

+1 for this feature. Yes, it is easy to avoid test dependencies with enough experience and/or working alone, but this is not always the case.

For those interested in this feature, they can send PRs against the randomization branch to help finish what's left.

+1 for the feature. Really appreciate that a branch is in progress for this.

Still waiting on this :))

This can be really useful.
@tj I understand that is easy to avoid test dependencies when you work with people with some basic skills about testing, but sometimes you need to take over a development team and you can bump with people with not even basic knowledge about test cases.

In fact, this is also useful when you take over existent projects and want to easily check if one test is tied to the previos one.

@boneskull Great work! What's the status of this fix? Do you need help in anything?

I just wanted to share my temporary solution that I use for running mocha tests in random order. Maybe it will be useful for someone.

mocha $(find tests/ -name *.spec.js | shuf)

Unfortunately that doesn't shuffle test examples within the same example, but that's still pretty clever and handy!

+1 in support of this feature

This is still on the table, but needs attention from not-me

So, what's actually left here? Where can I start?

Would love to see that implemented ❤️

I just found the choma package, which provides a very simple plugin for Mocha to randomize the order of test suites and cases. Good alternative to rocha, which was mentioned earlier. Simple and solves the problem for me!

An alternative would be to run tests in parallel:

• Karma (+ mocha or jasmine) - karma-parallel - at this moment doesn't support code coverage
• Mocha - mocha-parallel-tests or mocha.parallel
• Jest - does this by default