Which Karma configuration prevents browser timeout during long-running test suites?

Answer

Use browserNoActivityTimeout in karma.conf.js. This setting tells the Karma server how long to wait for test activity from a connected browser before marking that browser as disconnected and failing the run. For long-running suites, raise it above the longest expected silent period between test results.

Confirmed facts and likely explanation

Confirmed:

• browserNoActivityTimeout governs inactivity during an active test run.
• captureTimeout governs only the initial browser connection and client-file execution.
• browserDisconnectTimeout and browserDisconnectTolerance tolerate brief socket drops, not extended silence.
• singleRun controls whether Karma exits after completion; it does not extend any timeout.

Likely explanation: If a browser disconnects mid-suite, Karma probably stopped receiving activity within the default browserNoActivityTimeout window. If it disconnects immediately after launch, captureTimeout is the more likely cause.

Configuration steps

1. Open karma.conf.js.
2. Set or increase browserNoActivityTimeout, for example to 120000 milliseconds.
3. If browsers fail to start in constrained CI, also increase captureTimeout.
4. Run the suite and inspect Karma server output for disconnection messages.

module.exports = function (config) {
  config.set({
    browserNoActivityTimeout: 120000,
    captureTimeout: 120000,
    singleRun: true
  });
};

Verification and assumptions

Default values vary by Karma version, so check the installed package or generated config before assuming a specific default. Setting the timeout too high can mask real hangs and delay CI failure detection. Reverse proxies in CI may also impose independent idle timeouts that Karma cannot control.

One missing diagnostic detail: does the disconnection happen during initial browser capture or after tests have started running? This determines whether captureTimeout or browserNoActivityTimeout needs adjustment.