add alert restore time check

Signed-off-by: Ben Ye <[email protected]>

test/e2e/rule_test.go

@@ -658,16 +658,18 @@ func TestStatelessRulerAlertStateRestore(t *testing.T) {
 		testutil.Ok(t, err)
 		if len(alerts) > 0 {
 			if alerts[0].State == rulespb.AlertState_FIRING {
-				return nil
+				// The second ruler alert's active at time is the same as the previous one,
+				// which means the alert state is restored successfully.
+				if alertActiveAt.Unix() == alerts[0].ActiveAt.Unix() {
+					return nil
+				} else {
+					return fmt.Errorf("alert active time is not restored")
+				}
 			}
 		}
 		return fmt.Errorf("alert is not firing")
 	})
 	testutil.Ok(t, err)
-
-	// The second ruler alert's active at time is the same as the previous one,
-	// which means the alert state is restored successfully.
-	testutil.Equals(t, alertActiveAt.Unix(), alerts[0].ActiveAt.Unix())
 }
 
 // TestRule_CanPersistWALData checks that in stateless mode, Thanos Ruler can persist rule evaluations