Add regression test for mock timer Reset() bug and fix it.

timing/timing.go

@@ -168,11 +168,7 @@ func removeMockTimer(t *mockTimer) bool {
 
 	if found {
 		// We found the given timer. Remove it.
-		if idx == len(mockTimers)-1 {
-			mockTimers = mockTimers[:idx]
-		} else {
-			mockTimers = append(mockTimers[:idx], mockTimers[idx+1])
-		}
+		mockTimers = append(mockTimers[:idx], mockTimers[idx+1:]...)
 		return true
 	} else {
 		// The timer was not present, indicating that it was already expired.

timing/timing_test.go

@@ -137,3 +137,43 @@ func TestNotExpiredReset(t *testing.T) {
 		t.Fatal("Timer didn't fire at it's new end time after being reset.")
 	}
 }
+
+// This is a regression test for a bug where:
+//  - Create 3 timers.
+//  - Reset() the first one.
+//  - The third timer is now no longer tracked and won't fire.
+func TestThreeTimersWithReset(t *testing.T) {
+	MockMode = true
+	timer1 := NewTimer(1 * time.Second)
+	done1 := make(chan struct{})
+
+	timer2 := NewTimer(2 * time.Second)
+	done2 := make(chan struct{})
+
+	timer3 := NewTimer(3 * time.Second)
+	done3 := make(chan struct{})
+
+	go func() {
+		<-timer1.C()
+		done1 <- struct{}{}
+	}()
+
+	go func() {
+		<-timer2.C()
+		done2 <- struct{}{}
+	}()
+
+	go func() {
+		<-timer3.C()
+		done3 <- struct{}{}
+	}()
+
+	timer1.Reset(4 * time.Second)
+
+	Elapse(2 * time.Second)
+	<-done2
+
+	Elapse(1 * time.Second)
+	// Panic here if bug exists.
+	<-done3
+}