diff --git a/tests/services/discussionCountService.test.mjs b/tests/services/discussionCountService.test.mjs
new file mode 100644
index 00000000..278ad97d
--- /dev/null
+++ b/tests/services/discussionCountService.test.mjs
@@ -0,0 +1,192 @@
+import { describe, test, mock, before, after, beforeEach } from "node:test";
+import assert from "node:assert/strict";
+import { createUiDom } from "../ui/helpers/jsdom-test-helpers.mjs";
+import DiscussionCountService from "../../js/services/discussionCountService.js";
+
+describe("DiscussionCountService", () => {
+  let dom;
+  let document;
+  let window;
+
+  before(() => {
+    dom = createUiDom();
+    window = dom.window;
+    document = dom.document;
+  });
+
+  after(() => {
+    dom.cleanup();
+  });
+
+  test("initialization sets defaults", () => {
+    const service = new DiscussionCountService();
+    assert.equal(service.maxVideos, 24);
+    assert.ok(service.logger);
+    assert.equal(service.videoDiscussionCountCache.size, 0);
+    assert.equal(service.inFlightDiscussionCounts.size, 0);
+  });
+
+  test("refreshCounts returns early if videos array is empty or invalid", () => {
+    const service = new DiscussionCountService();
+    // mock logger to ensure no warnings
+    const logger = { warn: mock.fn() };
+    service.logger = logger;
+
+    service.refreshCounts([], {});
+    service.refreshCounts(null, {});
+
+    assert.equal(service.inFlightDiscussionCounts.size, 0);
+    assert.equal(logger.warn.mock.callCount(), 0);
+  });
+
+  test("refreshCounts returns early if dependencies are missing", () => {
+      const service = new DiscussionCountService();
+      const video = { id: "video1" };
+
+      // Missing nostrClient
+      service.refreshCounts([video], { videoListRoot: document.createElement("div") });
+      assert.equal(service.inFlightDiscussionCounts.size, 0);
+
+      // Missing videoListRoot
+      service.refreshCounts([video], { nostrClient: {} });
+      assert.equal(service.inFlightDiscussionCounts.size, 0);
+  });
+
+  test("refreshCounts handles happy path (fetches and updates DOM)", async () => {
+    const service = new DiscussionCountService();
+    const video = { id: "video1", kind: 30078, pubkey: "pubkey1" };
+
+    const root = document.createElement("div");
+    const container = document.createElement("div");
+    container.dataset.discussionCount = "video1";
+    const valueEl = document.createElement("span");
+    valueEl.dataset.discussionCountValue = "true";
+    container.appendChild(valueEl);
+    root.appendChild(container);
+
+    const nostrClient = {
+        pool: {},
+        countEventsAcrossRelays: mock.fn(async () => ({
+          total: 42,
+          ok: true,
+          perRelay: [{ ok: true }]
+        }))
+    };
+
+    service.refreshCounts([video], { videoListRoot: root, nostrClient });
+
+    // Wait for promise resolution (microtasks)
+    await new Promise(resolve => process.nextTick(resolve));
+    await new Promise(resolve => process.nextTick(resolve));
+
+    assert.equal(nostrClient.countEventsAcrossRelays.mock.callCount(), 1);
+    assert.equal(valueEl.textContent, "42");
+    assert.equal(container.dataset.countState, "ready");
+    assert.equal(service.videoDiscussionCountCache.get("video1"), 42);
+  });
+
+  test("refreshCounts uses cached count if available", async () => {
+      const service = new DiscussionCountService();
+      const video = { id: "video1" };
+      service.videoDiscussionCountCache.set("video1", 100);
+
+      const root = document.createElement("div");
+      const container = document.createElement("div");
+      container.dataset.discussionCount = "video1";
+      const valueEl = document.createElement("span");
+      valueEl.dataset.discussionCountValue = "true";
+      container.appendChild(valueEl);
+      root.appendChild(container);
+
+      const nostrClient = {
+          pool: {},
+          countEventsAcrossRelays: mock.fn()
+      };
+
+      service.refreshCounts([video], { videoListRoot: root, nostrClient });
+
+      assert.equal(nostrClient.countEventsAcrossRelays.mock.callCount(), 0);
+      assert.equal(valueEl.textContent, "100");
+  });
+
+  test("refreshCounts handles API errors gracefully", async () => {
+      const logger = { warn: mock.fn() };
+      const service = new DiscussionCountService({ logger });
+      const video = { id: "video1" };
+
+      const root = document.createElement("div");
+      const container = document.createElement("div");
+      container.dataset.discussionCount = "video1";
+      const valueEl = document.createElement("span");
+      valueEl.dataset.discussionCountValue = "true";
+      container.appendChild(valueEl);
+      root.appendChild(container);
+
+      const error = new Error("Network error");
+      const nostrClient = {
+          pool: {},
+          countEventsAcrossRelays: mock.fn(async () => { throw error; })
+      };
+
+      service.refreshCounts([video], { videoListRoot: root, nostrClient });
+
+      const requestPromise = service.inFlightDiscussionCounts.get("video1");
+      await assert.rejects(requestPromise, error);
+
+      assert.equal(logger.warn.mock.callCount(), 1);
+      assert.equal(container.dataset.countState, "error");
+      assert.equal(valueEl.textContent, "—");
+  });
+
+  test("refreshCounts handles partial results", async () => {
+    const service = new DiscussionCountService();
+    const video = { id: "video1" };
+
+    const root = document.createElement("div");
+    const container = document.createElement("div");
+    container.dataset.discussionCount = "video1";
+    const valueEl = document.createElement("span");
+    valueEl.dataset.discussionCountValue = "true";
+    container.appendChild(valueEl);
+    root.appendChild(container);
+
+    const nostrClient = {
+        pool: {},
+        countEventsAcrossRelays: mock.fn(async () => ({ total: 5, partial: true, ok: true, perRelay: [{ ok: true }] }))
+    };
+
+    service.refreshCounts([video], { videoListRoot: root, nostrClient });
+
+    await new Promise(resolve => process.nextTick(resolve));
+    await new Promise(resolve => process.nextTick(resolve));
+
+    assert.equal(container.dataset.countState, "partial");
+    assert.equal(valueEl.textContent, "5");
+  });
+
+  test("refreshCounts handles unsupported relays (empty perRelay)", async () => {
+    const service = new DiscussionCountService();
+    const video = { id: "video1" };
+
+    const root = document.createElement("div");
+    const container = document.createElement("div");
+    container.dataset.discussionCount = "video1";
+    const valueEl = document.createElement("span");
+    valueEl.dataset.discussionCountValue = "true";
+    container.appendChild(valueEl);
+    root.appendChild(container);
+
+    const nostrClient = {
+        pool: {},
+        countEventsAcrossRelays: mock.fn(async () => ({ total: 0, perRelay: [] }))
+    };
+
+    service.refreshCounts([video], { videoListRoot: root, nostrClient });
+
+    await new Promise(resolve => process.nextTick(resolve));
+    await new Promise(resolve => process.nextTick(resolve));
+
+    assert.equal(container.dataset.countState, "unsupported");
+    assert.equal(valueEl.textContent, "—");
+  });
+});