diff --git a/tests/utils/videoTimestamps.test.mjs b/tests/utils/videoTimestamps.test.mjs
new file mode 100644
index 00000000..4c3060d1
--- /dev/null
+++ b/tests/utils/videoTimestamps.test.mjs
@@ -0,0 +1,187 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import {
+  getVideoRootIdentifier,
+  applyRootTimestampToVideosMap,
+  syncActiveVideoRootTimestamp,
+} from "../../js/utils/videoTimestamps.js";
+
+test("getVideoRootIdentifier", async (t) => {
+  await t.test("returns empty string for invalid inputs", () => {
+    assert.equal(getVideoRootIdentifier(null), "");
+    assert.equal(getVideoRootIdentifier(undefined), "");
+    assert.equal(getVideoRootIdentifier(123), "");
+    assert.equal(getVideoRootIdentifier("string"), "");
+    assert.equal(getVideoRootIdentifier({}), "");
+  });
+
+  await t.test("returns videoRootId when present", () => {
+    const video = { videoRootId: "root-123", id: "id-456" };
+    assert.equal(getVideoRootIdentifier(video), "root-123");
+  });
+
+  await t.test("returns id when videoRootId is missing", () => {
+    const video = { id: "id-456" };
+    assert.equal(getVideoRootIdentifier(video), "id-456");
+  });
+
+  await t.test("returns id when videoRootId is not a string", () => {
+    const video = { videoRootId: 123, id: "id-456" };
+    assert.equal(getVideoRootIdentifier(video), "id-456");
+  });
+});
+
+test("applyRootTimestampToVideosMap", async (t) => {
+  await t.test("returns early if videosMap is not a Map", () => {
+    // Should not throw
+    applyRootTimestampToVideosMap({ videosMap: {}, video: { id: "1" }, timestamp: 100 });
+  });
+
+  await t.test("updates rootCreatedAt for matching video ID", () => {
+    const map = new Map();
+    const videoObj = { id: "1", rootCreatedAt: 0 };
+    map.set("1", videoObj);
+
+    applyRootTimestampToVideosMap({
+      videosMap: map,
+      video: { id: "1" },
+      timestamp: 100,
+    });
+
+    assert.equal(videoObj.rootCreatedAt, 100);
+  });
+
+  await t.test("updates rootCreatedAt for other videos with same rootId", () => {
+    const map = new Map();
+    const video1 = { id: "1", videoRootId: "root-A", rootCreatedAt: 0 };
+    const video2 = { id: "2", videoRootId: "root-A", rootCreatedAt: 0 };
+    const video3 = { id: "3", videoRootId: "root-B", rootCreatedAt: 0 };
+
+    map.set("1", video1);
+    map.set("2", video2);
+    map.set("3", video3);
+
+    // video argument here acts as the trigger source
+    // In the implementation:
+    // 1. existing = map.get(video.id) -> updated
+    // 2. Loop over map -> if storedRootId === rootId -> updated
+
+    // Let's say we update for video 1, with rootId="root-A"
+    applyRootTimestampToVideosMap({
+      videosMap: map,
+      video: { id: "1" },
+      rootId: "root-A",
+      timestamp: 200,
+    });
+
+    assert.equal(video1.rootCreatedAt, 200);
+    assert.equal(video2.rootCreatedAt, 200); // Shares root-A
+    assert.equal(video3.rootCreatedAt, 0);   // Different root
+  });
+
+  await t.test("skips invalid stored objects in map", () => {
+    const map = new Map();
+    map.set("1", null);
+    map.set("2", "string");
+
+    // Should not throw
+    applyRootTimestampToVideosMap({
+      videosMap: map,
+      video: { id: "99" }, // not in map
+      rootId: "root-A",
+      timestamp: 300,
+    });
+  });
+});
+
+test("syncActiveVideoRootTimestamp", async (t) => {
+  await t.test("returns false for invalid timestamp", () => {
+    const res = syncActiveVideoRootTimestamp({
+      activeVideo: {},
+      timestamp: null,
+    });
+    assert.equal(res, false);
+  });
+
+  await t.test("returns false for invalid activeVideo", () => {
+    const res = syncActiveVideoRootTimestamp({
+      activeVideo: null,
+      timestamp: 100,
+    });
+    assert.equal(res, false);
+  });
+
+  await t.test("returns false if activeVideo has no root identifier", () => {
+    const res = syncActiveVideoRootTimestamp({
+      activeVideo: { foo: "bar" }, // no id or videoRootId
+      timestamp: 100,
+    });
+    assert.equal(res, false);
+  });
+
+  await t.test("returns false if rootId mismatch", () => {
+    const video = { id: "vid-1" }; // rootId will be "vid-1"
+    const res = syncActiveVideoRootTimestamp({
+      activeVideo: video,
+      rootId: "other-root",
+      timestamp: 100,
+    });
+    assert.equal(res, false);
+  });
+
+  await t.test("returns false if timestamp already matches", () => {
+    const video = { id: "vid-1", rootCreatedAt: 100 };
+    const res = syncActiveVideoRootTimestamp({
+      activeVideo: video,
+      timestamp: 100.5, // floors to 100
+    });
+    assert.equal(res, false);
+  });
+
+  await t.test("updates activeVideo and displayTags", () => {
+    const video = {
+      id: "vid-1",
+      tags: [["t", "tag1"]],
+      displayTags: [],
+      rootCreatedAt: 0
+    };
+
+    const res = syncActiveVideoRootTimestamp({
+      activeVideo: video,
+      timestamp: 123.456,
+    });
+
+    assert.equal(res, true);
+    assert.equal(video.rootCreatedAt, 123);
+    // collectVideoTags should have run
+    assert.ok(Array.isArray(video.displayTags));
+    assert.ok(video.displayTags.includes("tag1"));
+  });
+
+  await t.test("calls videoModal.updateMetadata if provided", () => {
+    const video = { id: "vid-1", created_at: 500 };
+    let called = false;
+
+    const buildPayload = ({ postedAt, editedAt }) => {
+      return { postedAt, editedAt };
+    };
+
+    const videoModal = {
+      updateMetadata: ({ timestamps, tags }) => {
+        called = true;
+        assert.equal(timestamps.postedAt, 1000);
+        assert.equal(timestamps.editedAt, 500);
+        assert.ok(tags);
+      }
+    };
+
+    syncActiveVideoRootTimestamp({
+      activeVideo: video,
+      timestamp: 1000,
+      buildModalTimestampPayload: buildPayload,
+      videoModal: videoModal,
+    });
+
+    assert.equal(called, true);
+  });
+});