Heads Up! You're viewing the docs for v3.0, an old version of Karma. v6.3 is the newest.


How Do I Debug a karma issue? #

Many issues can be solved by reading the debug log or by using the browsers devtools:

Use --log-level debug to investigate server-side issues, especially configuration issues. #

The DEBUG log includes a copy of the final 'config': note that plugins can alter the config and sometimes the settings you applied do not give the result you expected. The log includes both core karma lines and lines from plugins: use the logging prefix to determine if your issue may need to be reported to a karma plugin.

Use --no-single-run to investigate browser-side issues, especially global errors in test files. #

The --no-single-run option causes the server to print a URL and wait. Open the URL in a browser and use the browsers devtools to investigate the problem. Typically you will want to open the URL, then click the DEBUG link in the upper right corner. That opens a new window with cleaner code for debugging.

This is a common Windows issue, the compilation of the native ws module fails. Anyways, ws has a fallback JS implementation which NPM should take care using it. All you need to do is make sure that you're using an up-to-date version of NPM. To do that you can:

Update NPM #

$ npm install -g npm


Do a fresh NodeJS install #

If you have issues to update NPM, you can just go to the NodeJS download the current version. It will come with the latest NPM version.

The browser just does not start. What's going on? #

It's more likely Karma can't find the location of the browser binary (the execution file). You can fix this by setting the appropriate environment variable with the correct path (Google Chrome, for instance, uses the CHROME_BIN environment variable). Check out [browsers] for more information.

I'm getting a weird error from the browser, how can I debug it? #

Go to the captured browser and click the "DEBUG" button (or open http://localhost:9876/debug.html) and use the web inspector to see what's going on. (You may need to refresh the debug.html page for it to kick in once the web inspector is open.)

I'm getting a syntax error from a HTML file. It looks like the preprocessor isn't working. #

The patterns in the preprocessors configuration setting are resolved via the basePath setting. See preprocessors for more information. You can also turn on debug logging (use --log-level debug when starting Karma) and Karma will display which files are preprocessed.

I'm getting a npm ERR! peerinvalid Peer error. How can I fix that? #

Try to remove karma and karma-* modules from your node_modules first (for instance rm -rf /usr/local/lib/node_modules/karma-*), then install Karma again.

My tests are running really slow. What's going on? #

Make sure the Karma's tab is active. Browsers give inactive tabs only minimum CPU.


If you can't find the solution for your issue here you can also ask for help in the mailing-list or Stack Overflow.