labels: Extra tests and comment for WithoutLabels method. (#8024)

Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>

pkg/labels/labels.go

@@ -275,6 +275,7 @@ func (ls Labels) WithoutEmpty() Labels {
 		if v.Value != "" {
 			continue
 		}
+		// Do not copy the slice until it's necessary.
 		els := make(Labels, 0, len(ls)-1)
 		for _, v := range ls {
 			if v.Value != "" {

pkg/labels/labels_test.go

@@ -210,81 +210,83 @@ func TestLabels_HasDuplicateLabelNames(t *testing.T) {
 }
 
 func TestLabels_WithoutEmpty(t *testing.T) {
-	tests := []struct {
+	for _, test := range []struct {
 		input    Labels
 		expected Labels
 	}{
 		{
 			input: Labels{
-				{
-					Name:  "__name__",
-					Value: "test",
+				{Name: "foo"},
+				{Name: "bar"},
 			},
-				{
-					Name: "foo",
+			expected: Labels{},
 		},
 		{
-					Name:  "hostname",
-					Value: "localhost",
+			input: Labels{
+				{Name: "foo"},
+				{Name: "bar"},
+				{Name: "baz"},
 			},
-				{
-					Name: "bar",
+			expected: Labels{},
 		},
 		{
-					Name:  "job",
-					Value: "check",
-				},
+			input: Labels{
+				{Name: "__name__", Value: "test"},
+				{Name: "hostname", Value: "localhost"},
+				{Name: "job", Value: "check"},
 			},
 			expected: Labels{
-				{
-					Name:  "__name__",
-					Value: "test",
+				{Name: "__name__", Value: "test"},
+				{Name: "hostname", Value: "localhost"},
+				{Name: "job", Value: "check"},
 			},
-				{
-					Name:  "hostname",
-					Value: "localhost",
 		},
 		{
-					Name:  "job",
-					Value: "check",
+			input: Labels{
+				{Name: "__name__", Value: "test"},
+				{Name: "hostname", Value: "localhost"},
+				{Name: "bar"},
+				{Name: "job", Value: "check"},
 			},
+			expected: Labels{
+				{Name: "__name__", Value: "test"},
+				{Name: "hostname", Value: "localhost"},
+				{Name: "job", Value: "check"},
 			},
 		},
 		{
 			input: Labels{
-				{
-					Name:  "__name__",
-					Value: "test",
-				},
-				{
-					Name:  "hostname",
-					Value: "localhost",
-				},
-				{
-					Name:  "job",
-					Value: "check",
-				},
+				{Name: "__name__", Value: "test"},
+				{Name: "foo"},
+				{Name: "hostname", Value: "localhost"},
+				{Name: "bar"},
+				{Name: "job", Value: "check"},
 			},
 			expected: Labels{
-				{
-					Name:  "__name__",
-					Value: "test",
+				{Name: "__name__", Value: "test"},
+				{Name: "hostname", Value: "localhost"},
+				{Name: "job", Value: "check"},
 			},
-				{
-					Name:  "hostname",
-					Value: "localhost",
 		},
 		{
-					Name:  "job",
-					Value: "check",
+			input: Labels{
+				{Name: "__name__", Value: "test"},
+				{Name: "foo"},
+				{Name: "baz"},
+				{Name: "hostname", Value: "localhost"},
+				{Name: "bar"},
+				{Name: "job", Value: "check"},
 			},
+			expected: Labels{
+				{Name: "__name__", Value: "test"},
+				{Name: "hostname", Value: "localhost"},
+				{Name: "job", Value: "check"},
 			},
 		},
-	}
-
-	for i, test := range tests {
-		got := test.input.WithoutEmpty()
-		testutil.Equals(t, test.expected, got, "unexpected labelset for test case %d", i)
+	} {
+		t.Run("", func(t *testing.T) {
+			testutil.Equals(t, test.expected, test.input.WithoutEmpty())
+		})
 	}
 }