add test case for multiple TTL metadata.

tag/map.go

@@ -134,6 +134,9 @@ func Update(k Key, v string, mds ...Metadata) Mutator {
 // value if k doesn't exist already. It mutates the value
 // if k already exists.
 // Metadata applies metadata to the tag. It is optional.
+// Metadatas are applied in the order in which it is provided.
+// If more than one metadata updates the same attribute then
+// the update from the last metadata prevails.
 func Upsert(k Key, v string, mds ...Metadata) Mutator {
 	return &mutator{
 		fn: func(m *Map) (*Map, error) {

tag/map_test.go

@@ -260,6 +260,18 @@ func TestNewMapWithMetadata(t *testing.T) {
 			want: makeTestTagMapWithMetadata(
 				tagContent{"4", ttlNoPropMd}),
 		},
+		{
+			name: "from non-existing; upsert with multiple-metadata",
+			initial: makeTestTagMapWithMetadata(
+				tagContent{"5", ttlNoPropMd}),
+			mods: []Mutator{
+				Upsert(k4, "4", WithTTL(TTLUnlimitedPropagation), WithTTL(TTLNoPropagation)),
+				Upsert(k5, "5", WithTTL(TTLNoPropagation), WithTTL(TTLUnlimitedPropagation)),
+			},
+			want: makeTestTagMapWithMetadata(
+				tagContent{"4", ttlNoPropMd},
+				tagContent{"5", ttlUnlimitedPropMd}),
+		},
 		{
 			name:    "from empty; update invalid",
 			initial: nil,