go test — Hands-on Tasks¶

Go 1.21+. Each task has explicit acceptance criteria.

Task 1: Write and run a test¶

Create a function and a passing test.

Acceptance criteria - [ ] A _test.go file with func TestXxx(t *testing.T) exists. - [ ] go test prints ok. - [ ] go test -v shows the test name and PASS. - [ ] Introducing a bug makes it FAIL with a useful message and non-zero exit.

Task 2: Table-driven subtests¶

Convert a test to table-driven form.

Acceptance criteria - [ ] Multiple cases run via t.Run(name, ...). - [ ] go test -run 'TestX/<casename>' runs exactly one case. - [ ] go test -v shows each subtest separately.

Task 3: Observe and bypass the cache¶

See caching in action.

Acceptance criteria - [ ] A second go test shows (cached). - [ ] go test -count=1 re-runs (no (cached)). - [ ] go clean -testcache then go test re-runs.

Task 4: Catch a race¶

Write code with a data race and detect it.

Acceptance criteria - [ ] Two goroutines write a shared variable without synchronization. - [ ] go test may pass; go test -race reports DATA RACE. - [ ] Adding a mutex/channel makes -race clean.

Task 5: Coverage report¶

Generate and read coverage.

Acceptance criteria - [ ] go test -coverprofile=cover.out ./... writes the profile. - [ ] go tool cover -func=cover.out shows per-function coverage. - [ ] go tool cover -html=cover.out opens an annotated view.

Task 6: Benchmark and compare¶

Benchmark a function and compare two implementations.

Acceptance criteria - [ ] go test -bench=. -benchmem -run='^$' runs only benchmarks with alloc stats. - [ ] -count=10 produces enough samples for benchstat. - [ ] benchstat old.txt new.txt shows whether a change is a real improvement.

Task 7: Shuffle to find ordering bugs¶

Create an inter-test dependency and expose it.

Acceptance criteria - [ ] Two tests share package-level state so order matters. - [ ] go test -shuffle=on sometimes fails and prints a seed. - [ ] go test -shuffle=<seed> reproduces the failure. - [ ] Removing the shared state makes shuffling safe.

Task 8: Tag integration tests¶

Separate slow tests behind a build tag.

Acceptance criteria - [ ] An integration test is gated with //go:build integration. - [ ] go test ./... skips it; go test -tags=integration ./... runs it. - [ ] You explain why this keeps the inner loop fast.