diff --git a/services/mailer/mail_admin_new_user.go b/services/mailer/mail_admin_new_user.go
index aa0571e57c..54287b1b7e 100644
--- a/services/mailer/mail_admin_new_user.go
+++ b/services/mailer/mail_admin_new_user.go
@@ -19,14 +19,11 @@ const (
 	tplNewUserMail base.TplName = "notify/admin_new_user"
 )
 
-var sa = SendAsync
-
 // MailNewUser sends notification emails on new user registrations to all admins
 func MailNewUser(ctx context.Context, u *user_model.User) {
 	if !setting.Admin.SendNotificationEmailOnNewUser {
 		return
 	}
-
 	if setting.MailService == nil {
 		// No mail service configured
 		return
@@ -77,5 +74,5 @@ func mailNewUser(ctx context.Context, u *user_model.User, lang string, tos []str
 		msg.Info = subject
 		msgs = append(msgs, msg)
 	}
-	sa(msgs...)
+	SendAsync(msgs...)
 }
diff --git a/services/mailer/mail_admin_new_user_test.go b/services/mailer/mail_admin_new_user_test.go
index b89d888ee1..603a8b95c9 100644
--- a/services/mailer/mail_admin_new_user_test.go
+++ b/services/mailer/mail_admin_new_user_test.go
@@ -11,10 +11,12 @@ import (
 	"code.gitea.io/gitea/models/db"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/setting"
-	"code.gitea.io/gitea/modules/translation"
+	"code.gitea.io/gitea/modules/test"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	_ "github.com/mattn/go-sqlite3"
 )
 
 func getTestUsers(t *testing.T) []*user_model.User {
@@ -45,54 +47,35 @@ func cleanUpUsers(ctx context.Context, users []*user_model.User) {
 }
 
 func TestAdminNotificationMail_test(t *testing.T) {
-	translation.InitLocales(context.Background())
-	locale := translation.NewLocale("")
-	key := "mail.admin.new_user.user_info"
-	translatedKey := locale.Tr(key)
-	require.NotEqualValues(t, key, translatedKey)
-
-	mailService := setting.Mailer{
-		From:     "test@example.com",
-		Protocol: "dummy",
-	}
-
-	setting.MailService = &mailService
-
-	// test with SEND_NOTIFICATION_EMAIL_ON_NEW_USER enabled
-	setting.Admin.SendNotificationEmailOnNewUser = true
-
 	ctx := context.Background()
-	NewContext(ctx)
 
 	users := getTestUsers(t)
-	oldSendAsync := sa
-	defer func() {
-		sa = oldSendAsync
-		cleanUpUsers(ctx, users)
-	}()
 
-	called := false
-	sa = func(msgs ...*Message) {
-		assert.Equal(t, len(msgs), 1, "Test provides only one admin user, so only one email must be sent")
-		assert.Equal(t, msgs[0].To, users[0].Email, "checks if the recipient is the admin of the instance")
-		manageUserURL := setting.AppURL + "admin/users/" + strconv.FormatInt(users[1].ID, 10)
-		assert.Contains(t, msgs[0].Body, manageUserURL)
-		assert.Contains(t, msgs[0].Body, users[1].HTMLURL())
-		assert.Contains(t, msgs[0].Body, translatedKey, "the .Locale translates to nothing")
-		assert.Contains(t, msgs[0].Body, users[1].Name, "user name of the newly created user")
-		for _, untranslated := range []string{"mail.admin", "admin.users"} {
-			assert.NotContains(t, msgs[0].Body, untranslated, "this is an untranslated placeholder prefix")
-		}
-		called = true
-	}
-	MailNewUser(ctx, users[1])
-	assert.True(t, called)
+	t.Run("SendNotificationEmailOnNewUser_true", func(t *testing.T) {
+		defer test.MockVariableValue(&setting.Admin.SendNotificationEmailOnNewUser, true)()
 
-	// test with SEND_NOTIFICATION_EMAIL_ON_NEW_USER disabled; emails shouldn't be sent
-	setting.Admin.SendNotificationEmailOnNewUser = false
-	sa = func(msgs ...*Message) {
-		assert.Equal(t, 1, 0, "this shouldn't execute. MailNewUser must exit early since SEND_NOTIFICATION_EMAIL_ON_NEW_USER is disabled")
-	}
+		called := false
+		defer mockMailSettings(func(msgs ...*Message) {
+			assert.Equal(t, len(msgs), 1, "Test provides only one admin user, so only one email must be sent")
+			assert.Equal(t, msgs[0].To, users[0].Email, "checks if the recipient is the admin of the instance")
+			manageUserURL := setting.AppURL + "admin/users/" + strconv.FormatInt(users[1].ID, 10)
+			assert.Contains(t, msgs[0].Body, manageUserURL)
+			assert.Contains(t, msgs[0].Body, users[1].HTMLURL())
+			assert.Contains(t, msgs[0].Body, users[1].Name, "user name of the newly created user")
+			assertTranslatedLocale(t, msgs[0].Body, "mail.admin", "admin.users")
+			called = true
+		})()
+		MailNewUser(ctx, users[1])
+		assert.True(t, called)
+	})
 
-	MailNewUser(ctx, users[1])
+	t.Run("SendNotificationEmailOnNewUser_false", func(t *testing.T) {
+		defer test.MockVariableValue(&setting.Admin.SendNotificationEmailOnNewUser, false)()
+		defer mockMailSettings(func(msgs ...*Message) {
+			assert.Equal(t, 1, 0, "this shouldn't execute. MailNewUser must exit early since SEND_NOTIFICATION_EMAIL_ON_NEW_USER is disabled")
+		})()
+		MailNewUser(ctx, users[1])
+	})
+
+	cleanUpUsers(ctx, users)
 }
diff --git a/services/mailer/main_test.go b/services/mailer/main_test.go
index f803c736ca..399d05ac7b 100644
--- a/services/mailer/main_test.go
+++ b/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()
+		}
+	}
+}