fix copy comments to include document comments

kyaml/comments/comments_test.go

@@ -0,0 +1,65 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package comments
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+)
+
+func TestCopyComments(t *testing.T) {
+	from, err := yaml.Parse(`# A
+#
+# B
+
+# C
+apiVersion: apps/v1
+kind: Deployment
+spec: # comment 1
+  # comment 2
+  replicas: 3 # comment 3
+  # comment 4
+`)
+	if !assert.NoError(t, err) {
+		t.FailNow()
+	}
+
+	to, err := yaml.Parse(`apiVersion: apps/v1
+kind: Deployment
+spec:
+  replicas: 4
+`)
+	if !assert.NoError(t, err) {
+		t.FailNow()
+	}
+
+	err = CopyComments(from, to)
+	if !assert.NoError(t, err) {
+		t.FailNow()
+	}
+
+	actual, err := to.String()
+	if !assert.NoError(t, err) {
+		t.FailNow()
+	}
+
+	expected := `# A
+#
+# B
+
+# C
+apiVersion: apps/v1
+kind: Deployment
+spec: # comment 1
+  # comment 2
+  replicas: 4 # comment 3
+  # comment 4
+`
+
+	if !assert.Equal(t, expected, actual) {
+		t.FailNow()
+	}
+}