"karma run" re-runs preprocessors for unmodified files

[segrey]

Expected behaviour

Running tests via "karma run" should not run preprocessors for unmodified files.

Actual behaviour

Running tests via "karma run" always runs preprocessors for all files (including unmodified ones).

Environment Details

• Karma version (output of karma --version): 1.7.1
• Relevant part of your karma.config.js file: see steps to reproduce

Steps to reproduce the behaviour

1. Open https://github.com/babel/karma-babel-preprocessor/tree/v7.0.0 and update "karma" dependency to 1.7.1
2. Run karma server: ./node_modules/karma/bin/karma start
3. Run karma tests: ./node_modules/karma/bin/karma run
   Output:

...
19 09 2017 16:30:15.693:DEBUG [karma]: Refreshing all the files / patterns
19 09 2017 16:30:15.696:DEBUG [preprocessor.babel]: Processing "/home/segrey/samples/karma-babel-preprocessor/test/hello.js".
19 09 2017 16:30:15.728:DEBUG [preprocessor.babel]: Processing "/home/segrey/samples/karma-babel-preprocessor/test/generator.spec.js".
19 09 2017 16:30:15.735:DEBUG [preprocessor.babel]: Processing "/home/segrey/samples/karma-babel-preprocessor/test/hello.spec.js".
19 09 2017 16:30:15.741:DEBUG [preprocessor.babel]: Processing "/home/segrey/samples/karma-babel-preprocessor/test/generator.js".
...

Expected behaviour: unmodified files are not processed

[segrey]

This issue is relevant for WebStorm users, since it uses "karma run" for each test run. Related WebStorm issue: https://youtrack.jetbrains.com/issue/WEB-28736.

[S-K-A]

2 Months later. It would be nice if this could be worked on (or around ;-) ). Either here or for JetBrains karma integration.
We are not able to use latest WebStorm Versions when it comes to unit testing.
Most of the developers are forced to keep the 2017.1.4 Version to be able to run tests locally, because this is the last one working correctly.

[johnjbarton]

I wonder why you think unmodified files should not be preprocessed? In any case, the preprocessor plugin, not karma-runner, is responsible for preprocessing. Please ask about it on karma-babel-preprocessor.

[segrey]

@johnjbarton Correct, karma-babel-preprocessor is responsible for processing. However, I'm not sure it should be responsible for caching its response, e.g. checking file's last modified date. Or should it be?
Currently, fileList.refresh() does two things: re-globs all patterns and preprocesses all matched files. Why can the preprocessing of unmodified files be needed?

[maksimr]

@johnjbarton could you explain why karma should run preprocessors for unmodified files?

Thanks

[johnjbarton]

karma does not know anything about what the preprocessor does. How can it know whether a file needs to be preprocessed when another file is changed?

[segrey]

@johnjbarton Right, it's probably relevant for karma watcher as well, not only "karma run" command. Because fileList.changeFile(filePath) runs preprocessor for a changed file only (here), not for files dependent on the changed file. So, this issue is about synchronizing behavior of karma watcher and "karma run" to preprocess the same set of files for the same changed files.