Testing in Go: Table-Driven Tests, httptest and Benchmarks

Go's testing tools are built in: no framework to choose. Tests live next to the code in _test.go files.

Table-driven tests

// slug_test.go
func TestSlugify(t *testing.T) {
    tests := []struct {
        name, in, want string
    }{
        {"simple", "Hello World", "hello-world"},
        {"punctuation", "Go: Fast & Simple!", "go-fast-simple"},
        {"spaces", "  trim me  ", "trim-me"},
        {"empty", "", ""},
    }
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            if got := Slugify(tt.in); got != tt.want {
                t.Errorf("Slugify(%q) = %q, want %q", tt.in, got, tt.want)
            }
        })
    }
}

go test ./...                 # all packages
go test -run TestSlugify/punctuation -v
go test -race ./...           # detect data races
go test -cover ./...

Testing HTTP handlers

func TestGetBook(t *testing.T) {
    srv := newServer()   // returns an http.Handler
    req := httptest.NewRequest("GET", "/books/1", nil)
    rec := httptest.NewRecorder()

    srv.ServeHTTP(rec, req)

    if rec.Code != http.StatusOK {
        t.Fatalf("status = %d, want 200", rec.Code)
    }
    var b Book
    json.NewDecoder(rec.Body).Decode(&b)
    if b.Title == "" {
        t.Error("expected a title")
    }
}

httptest.NewServer starts a real local server, which is handy for testing HTTP clients against a fake API.

Benchmarks

func BenchmarkSlugify(b *testing.B) {
    for b.Loop() {               // Go 1.24+; older code uses: for i := 0; i < b.N; i++
        Slugify("Go: Fast & Simple!")
    }
}

go test -bench=. -benchmem

Helpers and cleanup

func newTestDB(t *testing.T) *sql.DB {
    t.Helper()                    // failures point at the caller's line
    db := openTempDB()
    t.Cleanup(func() { db.Close() })
    return db
}