diff --git a/extensions/feishu/src/reply-dispatcher.test.ts b/extensions/feishu/src/reply-dispatcher.test.ts
index f1d77c5c9ca..61120a20514 100644
--- a/extensions/feishu/src/reply-dispatcher.test.ts
+++ b/extensions/feishu/src/reply-dispatcher.test.ts
@@ -21,6 +21,33 @@ const addTypingIndicatorMock = vi.hoisted(() => vi.fn(async () => ({ messageId:
 const removeTypingIndicatorMock = vi.hoisted(() => vi.fn(async () => {}));
 const streamingInstances = vi.hoisted((): StreamingSessionStub[] => []);
 
+function mergeStreamingText(
+  previousText: string | undefined,
+  nextText: string | undefined,
+): string {
+  const previous = typeof previousText === "string" ? previousText : "";
+  const next = typeof nextText === "string" ? nextText : "";
+  if (!next) {
+    return previous;
+  }
+  if (!previous || next === previous) {
+    return next;
+  }
+  if (next.startsWith(previous) || next.includes(previous)) {
+    return next;
+  }
+  if (previous.startsWith(next) || previous.includes(next)) {
+    return previous;
+  }
+  const maxOverlap = Math.min(previous.length, next.length);
+  for (let overlap = maxOverlap; overlap > 0; overlap -= 1) {
+    if (previous.slice(-overlap) === next.slice(0, overlap)) {
+      return `${previous}${next.slice(overlap)}`;
+    }
+  }
+  return `${previous}${next}`;
+}
+
 vi.mock("./accounts.js", () => ({
   resolveFeishuAccount: resolveFeishuAccountMock,
   resolveFeishuRuntimeAccount: resolveFeishuAccountMock,
@@ -38,10 +65,9 @@ vi.mock("./typing.js", () => ({
   addTypingIndicator: addTypingIndicatorMock,
   removeTypingIndicator: removeTypingIndicatorMock,
 }));
-vi.mock("./streaming-card.js", async () => {
-  const actual = await vi.importActual<typeof import("./streaming-card.js")>("./streaming-card.js");
+vi.mock("./streaming-card.js", () => {
   return {
-    mergeStreamingText: actual.mergeStreamingText,
+    mergeStreamingText,
     FeishuStreamingSession: class {
       active = false;
       start = vi.fn(async () => {