Testing with vitest¶

ts_test compiles TypeScript test files and runs them with vitest inside the Bazel sandbox.

Setup¶

# BUILD.bazel
load("@rules_typescript//ts:defs.bzl", "ts_compile", "ts_test")
load("@rules_typescript//npm:defs.bzl", "node_modules")

ts_compile(
    name = "math",
    srcs = ["math.ts"],
    visibility = ["//visibility:private"],
)

node_modules(
    name = "node_modules",
    deps = ["@npm//:vitest"],
)

ts_test(
    name = "math_test",
    srcs = ["math.test.ts"],
    deps = [":math", "@npm//:vitest"],
    node_modules = ":node_modules",
)

bazel test //path/to:math_test

Attributes¶

Attribute	Type	Default	Description
`srcs`	`label_list`	required	`.ts`/`.tsx` test files
`deps`	`label_list`	`[]`	`ts_compile` or npm targets the tests import
`node_modules`	`label`	`None`	A `node_modules` target for runtime npm resolution
`vitest`	`label`	`None`	Explicit vitest binary label (auto-detected from `node_modules` when absent)
`runtime`	`label`	`None`	Per-target JS runtime binary override
`env`	`string_dict`	`{}`	Additional environment variables
`size`	`string`	`"medium"`	Bazel test size
`update_snapshots`	`bool`	`False`	When True, produces an executable that runs `vitest run --update` and writes snapshot files back to the source tree

Sharding¶

ts_test supports Bazel test sharding. Pass --test_sharding_strategy=explicit and set shard_count on the target to distribute test files across parallel runners.

Snapshot Testing¶

Vitest snapshot files (.snap) must live in the source tree, but the Bazel sandbox is read-only. Two supported workflows:

Recommended: update_snapshots = True

ts_test(
    name = "my_test",
    srcs = ["Button.test.tsx"],
    deps = [":button"],
    node_modules = ":node_modules",
)

ts_test(
    name = "update_snapshots",
    srcs = ["Button.test.tsx"],
    deps = [":button"],
    node_modules = ":node_modules",
    update_snapshots = True,  # produces an executable, not a test
)

To create or update snapshots:

bazel run //path/to:update_snapshots

Vitest runs with --update from the workspace root, so snapshot files are written to the correct __snapshots__ directory alongside your source files. Commit the resulting .snap files to version control.

Alternative: --sandbox_writable_path

bazel test //path/to:my_test \
  --sandbox_writable_path=$(pwd)/src/components/__snapshots__

Watch Mode¶

Use ibazel to watch test files and re-run them on every change:

# Install ibazel
go install github.com/bazelbuild/bazel-watcher/cmd/ibazel@latest

# Watch a single test target
ibazel test //path/to:my_test

# Watch all tests in the repo
ibazel test //...

ibazel monitors the build graph and re-runs tests whenever a source file or dependency changes. Only the affected targets are rebuilt and re-tested.

Build Feedback¶

To see which targets were (re)built or cached:

# Show results for up to 10 targets (default is 1)
bazel test //... --show_result=10

# Show results for all targets (unlimited)
bazel test //... --show_result=0

Add test --show_result=20 to .bazelrc for a persistent setting.