Fix flaky Test_ActivityTimeouts (#2325)

host/client_integration_test.go

@@ -468,9 +468,22 @@ func (s *clientIntegrationSuite) Test_ActivityTimeouts() {
 		info := activity.GetInfo(ctx)
 		if info.ActivityID == "Heartbeat" {
 			go func() {
+				// NOTE: due to client side heartbeat batching, heartbeat may be sent
+				// later than expected.
+				// e.g. if activity heartbeat timeout is 2s,
+				// and we call RecordHeartbeat() at 0s, 0.5s, 1s, 1.5s
+				// the client by default will send two heartbeats at 0s and 2*0.8=1.6s
+				// Now if when running the test, this heartbeat goroutine becomes slow,
+				// and call RecordHeartbeat() after 1.6s, then that heartbeat will be sent
+				// to server at 3.2s (the next batch).
+				// Since the entire activity will finish at 5s, there won't be
+				// any heartbeat timeout error.
+				// so here, we reduce the duration between two heartbeats, so that they are
+				// more likey be sent in the heartbeat batch at 1.6s
+				// (basically increasing the room for delay in heartbeat goroutine from 0.1s to 1s)
 				for i := 0; i < 4; i++ {
 					activity.RecordHeartbeat(ctx, i)
-					time.Sleep(500 * time.Millisecond)
+					time.Sleep(200 * time.Millisecond)
 				}
 			}()
 		}