Fix diff view style handling (#36324)

Fix #36323

routers/web/repo/middlewares_test.go

@@ -0,0 +1,59 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repo
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/services/contexttest"
+	"code.gitea.io/gitea/services/gitdiff"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDiffViewStyle(t *testing.T) {
+	unittest.PrepareTestEnv(t)
+
+	t.Run("AnonymousUser", func(t *testing.T) {
+		ctx, _ := contexttest.MockContext(t, "/any")
+		SetDiffViewStyle(ctx)
+		assert.Equal(t, gitdiff.DiffStyleUnified, GetDiffViewStyle(ctx))
+
+		ctx, _ = contexttest.MockContext(t, "/any?style=split")
+		SetDiffViewStyle(ctx)
+		assert.Equal(t, gitdiff.DiffStyleSplit, GetDiffViewStyle(ctx))
+
+		ctx, _ = contexttest.MockContext(t, "/any")
+		SetDiffViewStyle(ctx)
+		assert.Equal(t, gitdiff.DiffStyleUnified, GetDiffViewStyle(ctx)) // at the moment, anonymous users don't have a saved preference
+	})
+
+	t.Run("SignedInUser", func(t *testing.T) {
+		ctx, _ := contexttest.MockContext(t, "/any")
+		contexttest.LoadUser(t, ctx, 2)
+		SetDiffViewStyle(ctx)
+		assert.Equal(t, gitdiff.DiffStyleUnified, GetDiffViewStyle(ctx))
+
+		ctx, _ = contexttest.MockContext(t, "/any?style=split")
+		contexttest.LoadUser(t, ctx, 2)
+		SetDiffViewStyle(ctx)
+		assert.Equal(t, gitdiff.DiffStyleSplit, GetDiffViewStyle(ctx))
+
+		ctx, _ = contexttest.MockContext(t, "/any")
+		contexttest.LoadUser(t, ctx, 2)
+		SetDiffViewStyle(ctx)
+		assert.Equal(t, gitdiff.DiffStyleSplit, GetDiffViewStyle(ctx))
+
+		ctx, _ = contexttest.MockContext(t, "/any?style=unified")
+		contexttest.LoadUser(t, ctx, 2)
+		SetDiffViewStyle(ctx)
+		assert.Equal(t, gitdiff.DiffStyleUnified, GetDiffViewStyle(ctx))
+
+		ctx, _ = contexttest.MockContext(t, "/any")
+		contexttest.LoadUser(t, ctx, 2)
+		SetDiffViewStyle(ctx)
+		assert.Equal(t, gitdiff.DiffStyleUnified, GetDiffViewStyle(ctx))
+	})
+}