In this article, we analyze Istanbul usage in tRPC source code. I found this comment — istanbul ignore if. This hints that tRPC uses Istanbul.js, a tool that makes JavaScript test coverage simple.
This one took me a while to figure out that tRPC repository uses @vitest/coverage-istanbul, I was initially looking to see if there’s any scripts related to test defined in packages/clients but there were none.
After searching for istanbul across the codebase, that is when I saw Istanbul word in vitest.config.ts test scripts are defined in the root level’s package.json.
"test": "turbo codegen-tests && conc -c \"green,blue\" \"vitest run\" \"pnpm -F tests test-run:tsc\"",
"test-ci": "turbo codegen-tests && conc \"CI=true vitest run - coverage\" \"pnpm -F tests test-run:tsc\"",
"test-watch": "vitest",
Below is coverage object picked from vitest.config.ts:
coverage: {
provider: 'istanbul',
include: ['**/src/**'],
exclude: [
'**/www/**',
'**/examples/**',
// skip codecov for experimental features
// FIXME: delete me once they're stable
'**/next/src/app-dir/**',
'**/server/src/adapters/next-app-dir/**',
],
},
Vitest supports another provider as well, it is ‘v8’. By default, provider is set to v8.
Let’s what happens when test script is run:
test script:
"test": "turbo codegen-tests && conc -c \"green,blue\" \"vitest run\" \"pnpm -F tests test-run:tsc\"",
tRPC uses Turbo. Turbo is an incremental bundler and build system optimized for JavaScript and TypeScript, written in Rust.
turbo codegen-tests:
codegen-tests is a command defined in turbo.json and when you run this, it executes codegen-tests scripts defined in the packages. This is a monorepo setup.
codegen-scripts in packages:
- client/package.json
- next/package.json
- react-query/package.json
- server/package.json
conc -c
conc is a short alias for concurrently. Checkout concurrrently.
Below is an example usage of concurrently.
concurrently "command1 arg" "command2 arg"
(or)
conc "command1 arg" "command2 arg"
tRPC uses this below command:
conc -c \"green,blue\" \"vitest run\" \"pnpm -F tests test-run:tsc\"
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