add unit test to check label rule labels override

Signed-off-by: jessicagreben <jessicagrebens@gmail.com>

cmd/promtool/rules_test.go

@@ -207,3 +207,67 @@ func createMultiRuleTestFiles(path string) error {
 `
 	return ioutil.WriteFile(path, []byte(recordingRules), 0777)
 }
+
+// TestBackfillLabels confirms that the labels in the rule file override the labels from the metrics
+// received from Prometheus Query API, including the __name__ label.
+func TestBackfillLabels(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", "backfilldata")
+	require.NoError(t, err)
+	defer func() {
+		require.NoError(t, os.RemoveAll(tmpDir))
+	}()
+	ctx := context.Background()
+
+	start := time.Date(2009, time.November, 10, 6, 34, 0, 0, time.UTC)
+	mockAPISamples := []*model.SampleStream{
+		{
+			Metric: model.Metric{"name1": "override", "__name__": "override"},
+			Values: []model.SamplePair{{Timestamp: model.TimeFromUnixNano(start.UnixNano()), Value: 123}},
+		},
+	}
+	ruleImporter, err := newTestRuleImporter(ctx, start, tmpDir, mockAPISamples)
+	require.NoError(t, err)
+
+	path := filepath.Join(tmpDir, "test.file")
+	recordingRules := `groups:
+- name: group0
+  rules:
+  - record: rule1
+    expr:  ruleExpr
+    labels:
+        name1: val1
+`
+	require.NoError(t, ioutil.WriteFile(path, []byte(recordingRules), 0777))
+	errs := ruleImporter.loadGroups(ctx, []string{path})
+	for _, err := range errs {
+		require.NoError(t, err)
+	}
+
+	errs = ruleImporter.importAll(ctx)
+	for _, err := range errs {
+		require.NoError(t, err)
+	}
+
+	opts := tsdb.DefaultOptions()
+	opts.AllowOverlappingBlocks = true
+	db, err := tsdb.Open(tmpDir, nil, nil, opts, nil)
+	require.NoError(t, err)
+
+	q, err := db.Querier(context.Background(), math.MinInt64, math.MaxInt64)
+	require.NoError(t, err)
+
+	t.Run("correct-labels", func(t *testing.T) {
+		selectedSeries := q.Select(false, nil, labels.MustNewMatcher(labels.MatchRegexp, "", ".*"))
+		for selectedSeries.Next() {
+			series := selectedSeries.At()
+			expectedLabels := labels.Labels{
+				labels.Label{Name: "__name__", Value: "rule1"},
+				labels.Label{Name: "name1", Value: "val1"},
+			}
+			require.Equal(t, expectedLabels, series.Labels())
+		}
+		require.NoError(t, selectedSeries.Err())
+		require.NoError(t, q.Close())
+		require.NoError(t, db.Close())
+	})
+}