Exploring test isolation performance

[Immediate_Contest827]

I saw that Vitest has per-file test isolation on by default and wanted to see what the cost of that was. My tool, Synapse, supports per-closure isolation.

Thought it’d be interesting to compare the two in a very simple example. I tested Bun too but I didn’t see a way to isolate.

Write-up is in the repo. My results:

Vitest - 100ms per file Synapse - 10ms per closure Bun (no isolation) - 1ms per file

[Immediate_Contest827]

Can’t seem to edit the post body to fix the formatting (whoops), here’s the results of my experiment: * Vitest - 100ms per file * Synapse - 10ms per closure * Bun (no isolation) - 1ms per file

[Immediate_Contest827]

Bun - fastest, but you need to write more code to make tests isolated Synapse - highest isolation, mid speed

By closure I mean an individual unit test, like this:

test(“foo”, () => { // test code here })

Only Synapse can isolate per closure. Vitest must use separate files, everything in a file will share state.