karma-runner/karma

karma watch tends to fail with large streamed bundles

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#2420 opened on Oct 25, 2016

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 (2 comments) (0 reactions) (0 assignees)JavaScript (11,918 stars) (1,703 forks)batch import
help wantedtype: feature

Description

i currently use gulp to produce two large JS bundles from TypeScript with browserify and factor-bundle. One bundle has all the main code and the other has all the specs.

The problem is when I use watch mode and update the bundles, karma detects two file change events on both files. I notice karma picks up the first change where the file is empty. This is confirmed by doing a readFileSync around here. Additionally, the syntax error message from the test execution also confirms this (i.e. Unexpected end of input).

Setting autoWatchBatchDelay to a higher number doesn't mitigate this problem. There is usually a 0.5 second delay between the first change event (empty file) and the second one (file generated). I'm not exactly sure what's going on there (maybe there's a race condition somewhere?) I remember adding a console.log(self.files) somewhere in the aforementioned section of code and since the output is very long, it takes time to flush to the terminal and the problem stops occurring (however waiting a long time is not a very productive activity!)

By enabling awaitWriteFinish in chokidar, the problem is mitigated. Maybe this is the solution?

https://github.com/karma-runner/karma/compare/master...khoomeister:ck-awaitwritefinish#diff-3c250c1426c199f7eccf17c774f0adfaR84

It'd be great to find a permanent fix for this as this is vital to our TDD workflow.

Contributor guide

Tech stack
javascriptnodejs
Domain
testingtooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Knowledge of Node.js file systemFamiliarity with karma configuration
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
The issue describes a race condition where karma's watch mode reads an empty file during bundle updates. The user suggests enabling `awaitWriteFinish` in chokidar as a fix. Investigate the code at `lib/file list.js` around line 362 where `readFileSync` is called. Check the linked comparison branch (khoomeister:ck awaitwritefinish) for a proposed implementation. Consider whether adding `awaitWriteFinish` option to chokidar configuration resolves the issue without side effects.