cloudwatch: handle invalid time ranges

pkg/tsdb/cloudwatch/cloudwatch.go

@@ -211,8 +211,8 @@ func (e *CloudWatchExecutor) executeQuery(ctx context.Context, query *CloudWatch
 		return nil, err
 	}
 
-	if endTime.Before(startTime) {
-		return nil, fmt.Errorf("Invalid time range: End time can't be before start time")
+	if !startTime.Before(endTime) {
+		return nil, fmt.Errorf("Invalid time range: Start time must be before end time")
 	}
 
 	params := &cloudwatch.GetMetricStatisticsInput{

pkg/tsdb/cloudwatch/cloudwatch_test.go

 package cloudwatch
 
 import (
+	"context"
 	"testing"
 	"time"
 
+	"github.com/grafana/grafana/pkg/models"
+	"github.com/grafana/grafana/pkg/tsdb"
+
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/cloudwatch"
 	"github.com/grafana/grafana/pkg/components/null"
@@ -14,6 +18,24 @@ import (
 func TestCloudWatch(t *testing.T) {
 	Convey("CloudWatch", t, func() {
 
+		Convey("executeQuery", func() {
+			e := &CloudWatchExecutor{
+				DataSource: &models.DataSource{
+					JsonData: simplejson.New(),
+				},
+			}
+
+			Convey("End time before start time should result in error", func() {
+				_, err := e.executeQuery(context.Background(), &CloudWatchQuery{}, &tsdb.TsdbQuery{TimeRange: tsdb.NewTimeRange("now-1h", "now-2h")})
+				So(err.Error(), ShouldEqual, "Invalid time range: Start time must be before end time")
+			})
+
+			Convey("End time equals start time should result in error", func() {
+				_, err := e.executeQuery(context.Background(), &CloudWatchQuery{}, &tsdb.TsdbQuery{TimeRange: tsdb.NewTimeRange("now-1h", "now-1h")})
+				So(err.Error(), ShouldEqual, "Invalid time range: Start time must be before end time")
+			})
+		})
+
 		Convey("can parse cloudwatch json model", func() {
 			json := `
 				{