util: Add errwrap package

Simplify working with errors across our code base. Instead of constantly
importing the necessary error helpers, assemble them all into one
package and import and use that as needed.

util/errwrap/errwrap_test.go

@@ -0,0 +1,51 @@
+// Mgmt
+// Copyright (C) 2013-2018+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+// +build !root
+
+package errwrap
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestWrapfErr1(t *testing.T) {
+	if err := Wrapf(nil, "whatever: %d", 42); err != nil {
+		t.Errorf("expected nil result")
+	}
+}
+
+func TestAppendErr1(t *testing.T) {
+	if err := Append(nil, nil); err != nil {
+		t.Errorf("expected nil result")
+	}
+}
+
+func TestAppendErr2(t *testing.T) {
+	reterr := fmt.Errorf("reterr")
+	if err := Append(reterr, nil); err != reterr {
+		t.Errorf("expected reterr")
+	}
+}
+
+func TestAppendErr3(t *testing.T) {
+	err := fmt.Errorf("err")
+	if reterr := Append(nil, err); reterr != err {
+		t.Errorf("expected err")
+	}
+}