How to run tests
Next.js
Most Turbopack testing is done through integration tests in Next.js. Currently (as of February 2024), Turbopack does not pass all of the Next.js test cases. When running tests, some tests are not performed because of the distinction between Turbopack and traditional tests.
Turbopack test manifestcontains a list of tests that either pass or fail, and test runner selectively runs passing test on the CI.
In general, you can use CI to run full test cases and check for regressions, and run individual tests on your local machine in the following ways.
// Run single test file
TURBOPACK=1 pnpm test-dev test/e2e/edge-can-use-wasm-files/index.test.ts
// Run specific test case in the specified file
TURBOPACK=1 pnpm test-dev test/e2e/edge-can-use-wasm-files/index.test.ts -t "middleware can use wasm files lists the necessary wasm bindings in the manifest"
Few environment variable can control test's behavior.
// Run Next.js in Turbopack mode. Required when running Turbopack tests.
TURBOPACK=1
// Specifies the location of the next-swc napi binding binary.
// Allows to use locally changed turbopack binaries in certain app (i.e vercel/front) without replacing
// whole next.js installation
__INTERNAL_CUSTOM_TURBOPACK_BINDINGS=${absolute_path_to_node_bindings}
Updating test snapshot
Most of test cases have snapshot will have branching like below:
if (process.env.TURBOPACK) {
expect(some).toMatchInlineSnapshot(..)
} else {
expect(some).toMatchInlineSnapshot(..)
}
This allows you to test different output snapshots per bundler without changing snapshots. When there are changes in those snapshots, test should ran against webpack & Turbopack both to ensure both snapshots are reflecting changes.
Check the status of tests
There are few places we can track the status of tests.
Turbopack
Turbo have some tests for the Turbopack as well. It is recommended to use nextest to run the tests.
Test flakiness
Next.js and Turbopack's test both can be flaky. In most cases, retry CI couple of times would resolve the issue. If not and unsure, check in #team-turbopack or #coord-next-turbopack