test: fix flaky test

Helper method that performs initial assigning of master/replica roles
and is widely used in ConnectionPool tests was adjusted to wait for
the roles to be applied successfully.
Prior to this patch it doesn't, so sometimes subsequent test code might
work unexpectedly (the problem was caught with
TestConnectionHandlerOpenUpdateClose)

Closes #452

Author: elhimov

test_helpers/pool_helper.go

@@ -214,6 +214,50 @@ func SetInstanceRO(ctx context.Context, dialer tarantool.Dialer, connOpts tarant
 		return err
 	}
 
+	checkRole := func(conn *tarantool.Connection, isReplica bool) string {
+		data, err := conn.Do(tarantool.NewCallRequest("box.info")).Get()
+		switch {
+		case err != nil:
+			return fmt.Sprintf("failed to get box.info: %s", err)
+		case len(data) < 1:
+			return "box.info is empty"
+		}
+
+		boxInfo, ok := data[0].(map[interface{}]interface{})
+		if !ok {
+			return "unexpected type in box.info response"
+		}
+
+		status, statusFound := boxInfo["status"]
+		readonly, readonlyFound := boxInfo["ro"]
+		switch {
+		case !statusFound:
+			return "box.info.status is missing"
+		case status != "running":
+			return fmt.Sprintf("box.info.status='%s' (waiting for 'running')", status)
+		case !readonlyFound:
+			return "box.info.ro is missing"
+		case readonly != isReplica:
+			return fmt.Sprintf("box.info.ro='%v' (waiting for '%v')", readonly, isReplica)
+		default:
+			return ""
+		}
+	}
+
+	problem := "not checked yet"
+
+	// Wait for the role to be applied.
+	for len(problem) != 0 {
+		select {
+		case <-time.After(10 * time.Millisecond):
+		case <-ctx.Done():
+			return fmt.Errorf("%w: failed to apply role, the last problem: %s",
+				ctx.Err(), problem)
+		}
+
+		problem = checkRole(conn, isReplica)
+	}
+
 	return nil
 }