Add notifications package for easy sending of notifications (#779)

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/779
Co-authored-by: konrad <konrad@kola-entertainments.de>
Co-committed-by: konrad <konrad@kola-entertainments.de>

pkg/mail/testing.go

@@ -0,0 +1,48 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-2021 Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public Licensee 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 Affero General Public Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package mail
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+var (
+	isUnderTest bool
+	sentMails   []*Opts
+)
+
+// Fake stops any mails from being sent and instead allows for recording and querying them.
+func Fake() {
+	isUnderTest = true
+	sentMails = nil
+}
+
+// AssertSent asserts if a mail has been sent
+func AssertSent(t *testing.T, opts *Opts) {
+	var found bool
+	for _, testMail := range sentMails {
+		if reflect.DeepEqual(testMail, opts) {
+			found = true
+			break
+		}
+	}
+
+	assert.True(t, found, "Failed to assert mail '%v' has been sent.", opts)
+}