tests(services/mailer): refactor mail_admin_new_user_test

* use MockVariableValue where appropriate
* split the tests in two with t.Run for clarity

services/mailer/main_test.go

@@ -4,13 +4,45 @@
 package mailer
 
 import (
+	"context"
 	"testing"
 
 	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/templates"
+	"code.gitea.io/gitea/modules/test"
+	"code.gitea.io/gitea/modules/translation"
 
 	_ "code.gitea.io/gitea/models/actions"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestMain(m *testing.M) {
 	unittest.MainTest(m)
 }
+
+func assertTranslatedLocale(t *testing.T, message string, prefixes ...string) {
+	t.Helper()
+	for _, prefix := range prefixes {
+		assert.NotContains(t, message, prefix, "there is an untranslated locale prefix")
+	}
+}
+
+func mockMailSettings(send func(msgs ...*Message)) func() {
+	translation.InitLocales(context.Background())
+	subjectTemplates, bodyTemplates = templates.Mailer(context.Background())
+	mailService := setting.Mailer{
+		From: "test@gitea.com",
+	}
+	cleanups := []func(){
+		test.MockVariableValue(&setting.MailService, &mailService),
+		test.MockVariableValue(&setting.Domain, "localhost"),
+		test.MockVariableValue(&SendAsync, send),
+	}
+	return func() {
+		for _, cleanup := range cleanups {
+			cleanup()
+		}
+	}
+}