Testing Concurrency – Race Detector and `testing`

Testing Concurrent Code

This lesson explains the main concept clearly with beginner-friendly examples and background so you can learn why the code works.

Race Detector

Run tests with -race to catch data races.

$ go test -race ./...

Example: Concurrent Counter

type Counter struct { n int; mu sync.Mutex }
func (c *Counter) Inc() { c.mu.Lock(); c.n++; c.mu.Unlock() }
func (c *Counter) Value() int { c.mu.Lock(); defer c.mu.Unlock(); return c.n }

func TestCounter(t *testing.T) {
    var c Counter
    var wg sync.WaitGroup
    for i := 0; i < 1000; i++ {
        wg.Add(1)
        go func() { c.Inc(); wg.Done() }()
    }
    wg.Wait()
    if got := c.Value(); got != 1000 { t.Fatalf("got %d, want 1000", got) }
}

The race detector will flag any missing synchronization.