Add TransferSubGroup to transfer a group to a new parent group

groups.go

@@ -345,6 +345,40 @@ func (s *GroupsService) TransferGroup(gid interface{}, pid interface{}, options
 	return g, resp, err
 }
 
+// TransferSubGroupOptions represents the available TransferSubGroup() options.
+//
+// GitLab API docs:
+// https://docs.gitlab.com/ee/api/groups.html#transfer-a-group-to-a-new-parent-group--turn-a-subgroup-to-a-top-level-group
+type TransferSubGroupOptions struct {
+	GroupID *int `url:"group_id,omitempty" json:"group_id,omitempty"`
+}
+
+// TransferSubGroup transfers a group to a new parent group or turn a subgroup
+// to a top-level group. Available to administrators and users.
+//
+// GitLab API docs:
+// https://docs.gitlab.com/ee/api/groups.html#transfer-a-group-to-a-new-parent-group--turn-a-subgroup-to-a-top-level-group
+func (s *GroupsService) TransferSubGroup(gid interface{}, opt *TransferSubGroupOptions, options ...RequestOptionFunc) (*Group, *Response, error) {
+	group, err := parseID(gid)
+	if err != nil {
+		return nil, nil, err
+	}
+	u := fmt.Sprintf("groups/%s/transfer", PathEscape(group))
+
+	req, err := s.client.NewRequest(http.MethodPost, u, opt, options)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	g := new(Group)
+	resp, err := s.client.Do(req, g)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return g, resp, err
+}
+
 // UpdateGroupOptions represents the available UpdateGroup() options.
 //
 // GitLab API docs: https://docs.gitlab.com/ee/api/groups.html#update-group

groups_test.go

@@ -117,6 +117,31 @@ func TestTransferGroup(t *testing.T) {
 	}
 }
 
+func TestTransferSubGroup(t *testing.T) {
+	mux, server, client := setup(t)
+	defer teardown(server)
+
+	mux.HandleFunc("/api/v4/groups/1/transfer",
+		func(w http.ResponseWriter, r *http.Request) {
+			testMethod(t, r, http.MethodPost)
+			fmt.Fprintf(w, `{"id": 1, "parent_id": 2}`)
+		})
+
+	opt := &TransferSubGroupOptions{
+		GroupID: Int(2),
+	}
+
+	group, _, err := client.Groups.TransferSubGroup(1, opt)
+	if err != nil {
+		t.Errorf("Groups.TransferSubGroup returned error: %v", err)
+	}
+
+	want := &Group{ID: 1, ParentID: 2}
+	if !reflect.DeepEqual(group, want) {
+		t.Errorf("Groups.TransferSubGroup returned %+v, want %+v", group, want)
+	}
+}
+
 func TestDeleteGroup(t *testing.T) {
 	mux, server, client := setup(t)
 	defer teardown(server)