When karma is auto-watching files, karma-webpack causes tests to occasionally run twice, possibly OS X-only

[alanchrt]

I have a larger project set up using gulp with karma's watch to run tests on the fly.

I noticed that frequently when making updates to test files karma is watching, the tests get fired twice. After paring down my configurations, it looks like karma-webpack is the culprit.

I'm on OS X, so hopefully the repro works on whatever platform. Here are instructions/a barebones repo to isolate the issue and reproduce:

https://github.com/alanctkc/karma-webpack-watch-bug-repro#readme

Here's a comparison of the output I get simulating changes with and without the ['webpack'] preprocessor:

https://gist.github.com/alanctkc/79c2c4586f13f22bd8e6

Unfortunately, it doesn't seem to be super deterministic, so you might have to simulate changes a few times before seeing any duplicates. But, when the preprocessor is removed, there never seem to be any duplicate runs at all.

Any ideas?

[ColCh]

What if you add timeout ~ 400ms for watcher ?

[alanchrt]

Thanks, @ColCh. Bumping autoWatchBatchDelay up does help, and solves the immediate need for me.

Any ideas what about karma-webpack might trigger a change? Would just opening the JS files for reading be enough to cause it?

[dlindahl]

FWIW, this very same problem was reported in nikku/karma-browserify#67. The comment from @mattyfsh seems to have resolved the issue for me.

[joshwiens]

Issue has multiple resolutions. Resolving

[milimetric]

I got my config to work (it no longer runs tests twice) based on the browserify example mentioned above. Here it is for clarity:

{
    ...

    frameworks: ['jasmine-ajax', 'jasmine'],

    files: [{
        pattern: './test/**/*.spec.js',
        watched: false,
        included: true,
        served: true
    }],

    preprocessors: {
        './test/**/*.spec.js': ['webpack']
    }
}