diff --git a/extensions/mattermost/src/mattermost/directory.test.ts b/extensions/mattermost/src/mattermost/directory.test.ts
new file mode 100644
index 00000000000..dd4848c6094
--- /dev/null
+++ b/extensions/mattermost/src/mattermost/directory.test.ts
@@ -0,0 +1,172 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const {
+  listMattermostAccountIdsMock,
+  resolveMattermostAccountMock,
+  createMattermostClientMock,
+  fetchMattermostMeMock,
+} = vi.hoisted(() => {
+  return {
+    listMattermostAccountIdsMock: vi.fn(),
+    resolveMattermostAccountMock: vi.fn(),
+    createMattermostClientMock: vi.fn(),
+    fetchMattermostMeMock: vi.fn(),
+  };
+});
+
+vi.mock("./accounts.js", () => {
+  return {
+    listMattermostAccountIds: listMattermostAccountIdsMock,
+    resolveMattermostAccount: resolveMattermostAccountMock,
+  };
+});
+
+vi.mock("./client.js", () => {
+  return {
+    createMattermostClient: createMattermostClientMock,
+    fetchMattermostMe: fetchMattermostMeMock,
+  };
+});
+
+import { listMattermostDirectoryGroups, listMattermostDirectoryPeers } from "./directory.js";
+
+describe("mattermost directory", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("deduplicates channels across enabled accounts and skips failing accounts", async () => {
+    const clientA = {
+      token: "token-a",
+      request: vi
+        .fn()
+        .mockResolvedValueOnce([
+          { id: "chan-1", type: "O", name: "alerts", display_name: "Alerts" },
+          { id: "chan-2", type: "P", name: "ops", display_name: "Ops" },
+          { id: "chan-3", type: "D", name: "dm", display_name: "Direct" },
+        ]),
+    };
+    const clientB = {
+      token: "token-b",
+      request: vi.fn().mockRejectedValue(new Error("expired token")),
+    };
+    const clientC = {
+      token: "token-c",
+      request: vi.fn().mockResolvedValueOnce([
+        { id: "chan-2", type: "P", name: "ops", display_name: "Ops" },
+        { id: "chan-4", type: "O", name: "infra", display_name: "Infra" },
+      ]),
+    };
+
+    listMattermostAccountIdsMock.mockReturnValue(["default", "alerts", "infra"]);
+    resolveMattermostAccountMock.mockImplementation(({ accountId }) => {
+      if (accountId === "disabled") {
+        return { enabled: false };
+      }
+      return { enabled: true, botToken: `token-${accountId}`, baseUrl: "https://chat.example.com" };
+    });
+    createMattermostClientMock
+      .mockReturnValueOnce(clientA)
+      .mockReturnValueOnce(clientB)
+      .mockReturnValueOnce(clientC);
+    fetchMattermostMeMock.mockResolvedValue({ id: "me-1" });
+
+    await expect(
+      listMattermostDirectoryGroups({
+        cfg: {} as never,
+        runtime: {} as never,
+        query: "  op  ",
+      }),
+    ).resolves.toEqual([{ kind: "group", id: "channel:chan-2", name: "ops", handle: "Ops" }]);
+  });
+
+  it("uses the first healthy client for peers and filters self and blanks", async () => {
+    const client = {
+      token: "token-default",
+      request: vi
+        .fn()
+        .mockResolvedValueOnce([{ id: "team-1" }])
+        .mockResolvedValueOnce([
+          { user_id: "me-1" },
+          { user_id: "user-1" },
+          { user_id: "user-2" },
+        ])
+        .mockResolvedValueOnce([
+          {
+            id: "user-1",
+            username: "alice",
+            first_name: "Alice",
+            last_name: "Ng",
+          },
+          {
+            id: "user-2",
+            username: "bob",
+            nickname: "Bobby",
+          },
+          {
+            id: "me-1",
+            username: "self",
+          },
+        ]),
+    };
+
+    listMattermostAccountIdsMock.mockReturnValue(["default"]);
+    resolveMattermostAccountMock.mockReturnValue({
+      enabled: true,
+      botToken: "token-default",
+      baseUrl: "https://chat.example.com",
+    });
+    createMattermostClientMock.mockReturnValue(client);
+    fetchMattermostMeMock.mockResolvedValue({ id: "me-1" });
+
+    await expect(
+      listMattermostDirectoryPeers({
+        cfg: {} as never,
+        runtime: {} as never,
+      }),
+    ).resolves.toEqual([
+      { kind: "user", id: "user:user-1", name: "alice", handle: "Alice Ng" },
+      { kind: "user", id: "user:user-2", name: "bob", handle: "Bobby" },
+    ]);
+  });
+
+  it("uses user search when a query is present and applies limits", async () => {
+    const client = {
+      token: "token-default",
+      request: vi
+        .fn()
+        .mockResolvedValueOnce([{ id: "team-1" }])
+        .mockResolvedValueOnce([
+          { id: "user-1", username: "alice", first_name: "Alice", last_name: "Ng" },
+          { id: "user-2", username: "alex", nickname: "Lex" },
+        ]),
+    };
+
+    listMattermostAccountIdsMock.mockReturnValue(["default"]);
+    resolveMattermostAccountMock.mockReturnValue({
+      enabled: true,
+      botToken: "token-default",
+      baseUrl: "https://chat.example.com",
+    });
+    createMattermostClientMock.mockReturnValue(client);
+    fetchMattermostMeMock.mockResolvedValue({ id: "me-1" });
+
+    await expect(
+      listMattermostDirectoryPeers({
+        cfg: {} as never,
+        runtime: {} as never,
+        query: "  ali  ",
+        limit: 1,
+      }),
+    ).resolves.toEqual([{ kind: "user", id: "user:user-1", name: "alice", handle: "Alice Ng" }]);
+
+    expect(client.request).toHaveBeenNthCalledWith(
+      2,
+      "/users/search",
+      expect.objectContaining({
+        method: "POST",
+        body: JSON.stringify({ term: "ali", team_id: "team-1" }),
+      }),
+    );
+  });
+});