Add unit test for `HashAvatar` (#25662)

- Add 100% unit test for this function.

---------

Co-authored-by: Gusted <postmaster@gusted.xyz>

modules/avatar/hash_test.go

@@ -0,0 +1,26 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package avatar_test
+
+import (
+	"bytes"
+	"image"
+	"image/png"
+	"testing"
+
+	"code.gitea.io/gitea/modules/avatar"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_HashAvatar(t *testing.T) {
+	myImage := image.NewRGBA(image.Rect(0, 0, 32, 32))
+	var buff bytes.Buffer
+	png.Encode(&buff, myImage)
+
+	assert.EqualValues(t, "9ddb5bac41d57e72aa876321d0c09d71090c05f94bc625303801be2f3240d2cb", avatar.HashAvatar(1, buff.Bytes()))
+	assert.EqualValues(t, "9a5d44e5d637b9582a976676e8f3de1dccd877c2fe3e66ca3fab1629f2f47609", avatar.HashAvatar(8, buff.Bytes()))
+	assert.EqualValues(t, "ed7399158672088770de6f5211ce15528ebd675e92fc4fc060c025f4b2794ccb", avatar.HashAvatar(1024, buff.Bytes()))
+	assert.EqualValues(t, "161178642c7d59eb25a61dddced5e6b66eae1c70880d5f148b1b497b767e72d9", avatar.HashAvatar(1024, []byte{}))
+}