Stabilizing importDurations (previously printImportBreakdown)

[sheremet-va]

experimental.importDurations

• Introduced in 4.0.15
• Docs:
  • Config option
  • Guide
• Related
  • Enhance importBreakdown support #9141
  • feat(experimental): add print and fail thresholds for importDurations #9533
• Rational:
  • We want to provide an easy way to analyze the performance of your tests. Specifically the "import" time (previously reported as "collected"). It is the time that took Vitest to import the test file, so it includes all the static imports.
  • Import breakdown shows a list of modules that took the longest to load, but it also provides a nice visualization in Vitest UI and the VSCode extension by showing a number next to the import (this is enabled by default even without this feature).
  • Our hope is that this information can help you (or your AI agent) debug the performance of your tests and refactor if necessary.

[mdubourg001]

Hey! First I want to say that this is a great idea to help debugging test performance issues. I myself tried to get such information for my project's test suite using a custom reporter and the importDurations object from the module given as parameter of the onTestModuleCollected hook. See the Gist here.

I computed average and total import times for each module in a rather simplistic way, and so I'm sure using the built-in printImportBreakdown will be much more precise, but I'd like to suggest to allow passing some configuration instead of just a boolean, for example:

export default defineConfig({
  // ...
  experimental: {
    printImportBreakdown: {
      top: 50, // show the Top 50 imports instead of the default 10
      onlyExternal: true // show only imports from `node_modules`
      // and maybe more ?
    }
  }
  // ...
})

[sheremet-va]

There are several improvements planned with the configuration: #9141

You can leave your ideas there too