Testing Concurrent Go with synctest

Sun, 16 Aug 2026 00:00:00 +0000

Notes from Alexander Baygeldin’s GopherCon 2026 talk, “(Sync)testing Concurrent Code with Confidence.”

Testing concurrent code used to mean picking one of three bad options: hacky (poke at internals), flaky (time.Sleep(100 * time.Millisecond) and hope), or slow (sleep long enough that it’s reliable). testing/synctest removes the tradeoff by giving the test a fake clock.

The fake clock

Inside synctest.Test, time doesn’t pass on its own. It jumps forward only when every goroutine in the bubble is blocked. A one-hour timeout resolves instantly and deterministically.

Table-Driven Tests in Go

Wed, 12 Aug 2026 00:00:00 +0000

Every Go codebase converges on the same test shape: a slice of cases, a loop, one t.Run per case. It is the closest thing Go has to a testing idiom, and it is worth writing deliberately rather than by habit.

The shape

func TestParseDuration(t *testing.T) {
 tests := []struct {
 name string
 give string
 want time.Duration
 wantErr string
 }{
 {
 name: "seconds",
 give: "30s",
 want: 30 * time.Second,
 },
 {
 name: "compound",
 give: "1h30m",
 want: 90 * time.Minute,
 },
 {
 name: "missing unit",
 give: "30",
 wantErr: "missing unit",
 },
 }

 for _, tt := range tests {
 t.Run(tt.name, func(t *testing.T) {
 got, err := ParseDuration(tt.give)
 if tt.wantErr != "" {
 require.ErrorContains(t, err, tt.wantErr)
 return
 }
 require.NoError(t, err)
 assert.Equal(t, tt.want, got)
 })
 }
}

Three things earn their place here.

Testing on Moises Vega

Testing Concurrent Go with synctest

The fake clock

Table-Driven Tests in Go

The shape