change output and related tests

scripts/metricsgen/metricsdiff/metricsdiff.go

@@ -168,14 +168,15 @@ func (m metricsList) Swap(i, j int)      { m[i], m[j] = m[j], m[i] }
 
 func (m Diff) String() string {
 	var s strings.Builder
+	if len(m.Adds) > 0 || len(m.Removes) > 0 {
+		fmt.Fprintln(&s, "Metric changes:")
+	}
 	if len(m.Adds) > 0 {
-		fmt.Fprintln(&s, "Adds:")
 		for _, add := range m.Adds {
 			fmt.Fprintf(&s, "+++ %s\n", add)
 		}
 	}
 	if len(m.Removes) > 0 {
-		fmt.Fprintln(&s, "Removes:")
 		for _, rem := range m.Removes {
 			fmt.Fprintf(&s, "--- %s\n", rem)
 		}
@@ -183,7 +184,7 @@ func (m Diff) String() string {
 	if len(m.Changes) > 0 {
 		fmt.Fprintln(&s, "Label changes:")
 		for _, ld := range m.Changes {
-			fmt.Fprintf(&s, "Label: %s\n", ld.Metric)
+			fmt.Fprintf(&s, "Metric: %s\n", ld.Metric)
 			for _, add := range ld.Adds {
 				fmt.Fprintf(&s, "+++ %s\n", add)
 			}

scripts/metricsgen/metricsdiff/metricsdiff_test.go

@@ -15,7 +15,7 @@ func TestDiff(t *testing.T) {
 		aContents string
 		bContents string
 
-		want metricsdiff.Diff
+		want string
 	}{
 		{
 			name: "labels",
@@ -25,15 +25,13 @@ func TestDiff(t *testing.T) {
 			bContents: `
 			metric_one{label_three="content", label_four="content"} 0
 			`,
-			want: metricsdiff.Diff{
-				Changes: []metricsdiff.LabelDiff{
-					{
-						Metric:  "metric_one",
-						Adds:    []string{"label_three", "label_four"},
-						Removes: []string{"label_one", "label_two"},
-					},
-				},
-			},
+			want: `Label changes:
+Metric: metric_one
++++ label_three
++++ label_four
+--- label_one
+--- label_two
+`,
 		},
 		{
 			name: "metrics",
@@ -43,10 +41,10 @@ func TestDiff(t *testing.T) {
 			bContents: `
 			metric_two{label_two="content"} 0
 			`,
-			want: metricsdiff.Diff{
-				Adds:    []string{"metric_two"},
-				Removes: []string{"metric_one"},
-			},
+			want: `Metric changes:
++++ metric_two
+--- metric_one
+`,
 		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
@@ -58,7 +56,7 @@ func TestDiff(t *testing.T) {
 			require.NoError(t, err)
 			md, err := metricsdiff.DiffFromReaders(bufA, bufB)
 			require.NoError(t, err)
-			require.Equal(t, tc.want, md)
+			require.Equal(t, tc.want, md.String())
 		})
 	}
 }