diff --git a/tests/integration/repo_sync_fork_test.go b/tests/integration/repo_sync_fork_test.go
new file mode 100644
index 0000000000000..e76003e0120e7
--- /dev/null
+++ b/tests/integration/repo_sync_fork_test.go
@@ -0,0 +1,71 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"testing"
+	"time"
+
+	auth_model "code.gitea.io/gitea/models/auth"
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+	api "code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/modules/util"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestRepoSyncFork(t *testing.T) {
+	onGiteaRun(t, func(*testing.T, *url.URL) {
+		forkUser := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 4})
+
+		baseRepo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+		baseUser := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: baseRepo.OwnerID})
+		repoString := baseUser.Name + "/" + baseRepo.Name
+
+		session := loginUser(t, forkUser.Name)
+		token := getTokenForLoggedInUser(t, session, auth_model.AccessTokenScopeWriteRepository)
+
+		checkSyncForkMessage := func(hasMessage bool, message string) {
+			require.Eventually(t, func() bool {
+				resp := session.MakeRequest(t, NewRequestf(t, "GET", "/%s/test-repo-fork", forkUser.Name), http.StatusOK)
+				htmlDoc := NewHTMLParser(t, resp.Body)
+				respMsg, _ := htmlDoc.Find(".ui.message").Html()
+				return strings.Contains(respMsg, message) != hasMessage
+			}, 5*time.Second, 100*time.Millisecond)
+		}
+
+		// create a fork
+		req := NewRequestWithJSON(t, "POST", fmt.Sprintf("/api/v1/repos/%s/forks", repoString), &api.CreateForkOption{
+			Name: util.ToPointer("test-repo-fork"),
+		}).AddTokenAuth(token)
+		MakeRequest(t, req, http.StatusAccepted)
+		forkRepo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{OwnerID: forkUser.ID, Name: "test-repo-fork"})
+
+		// Case 0: Update fork, should have no sync fork message
+		require.NoError(t, createOrReplaceFileInBranch(baseUser, baseRepo, "file0.txt", "master", "dummy"))
+		// the repo shows a prompt to "sync fork" and with precise commit count
+		checkSyncForkMessage(false, fmt.Sprintf(`<a href="/%v/src/branch/master">%v:master</a>`, repoString, repoString))
+
+		// Case 2: Base is ahead of fork
+		require.NoError(t, createOrReplaceFileInBranch(baseUser, baseRepo, "file1.txt", "master", "dummy"))
+		// the repo shows a prompt to "sync fork" and with precise commit count
+		checkSyncForkMessage(true, fmt.Sprintf(`This branch is 1 commit behind <a href="/%v/src/branch/master">%v:master</a>`, repoString, repoString))
+
+		// Case 3: Base has some commits that fork does not have, but fork updated
+		require.NoError(t, createOrReplaceFileInBranch(forkUser, forkRepo, "file2.txt", "master", "dummy"))
+		// the repo shows a prompt to "sync fork" and with just "new changes" text
+		checkSyncForkMessage(true, fmt.Sprintf(`The base branch <a href="/%v/src/branch/master">%v:master</a> has new changes`, repoString, repoString))
+
+		// Case 4: Base updates again
+		require.NoError(t, createOrReplaceFileInBranch(forkUser, forkRepo, "file3.txt", "master", "dummy"))
+		// the repo shows a prompt to "sync fork" and with just "new changes" text
+		checkSyncForkMessage(true, fmt.Sprintf(`The base branch <a href="/%v/src/branch/master">%v:master</a> has new changes`, repoString, repoString))
+	})
+}