diff --git a/src/create-managers.test.ts b/src/create-managers.test.ts
new file mode 100644
index 000000000..56f6e8cfc
--- /dev/null
+++ b/src/create-managers.test.ts
@@ -0,0 +1,101 @@
+/// <reference types="bun-types" />
+
+import { afterAll, beforeEach, describe, expect, it, mock } from "bun:test"
+
+const markServerRunningInProcess = mock(() => {})
+
+mock.module("./features/background-agent", () => ({
+  BackgroundManager: class BackgroundManager {
+    constructor(..._args: unknown[]) {}
+  },
+}))
+
+mock.module("./features/skill-mcp-manager", () => ({
+  SkillMcpManager: class SkillMcpManager {
+    constructor(..._args: unknown[]) {}
+  },
+}))
+
+mock.module("./features/task-toast-manager", () => ({
+  initTaskToastManager: mock(() => {}),
+}))
+
+mock.module("./features/tmux-subagent", () => ({
+  TmuxSessionManager: class TmuxSessionManager {
+    constructor(..._args: unknown[]) {}
+
+    async cleanup(): Promise<void> {}
+    async onSessionCreated(..._args: unknown[]): Promise<void> {}
+  },
+}))
+
+mock.module("./features/background-agent/process-cleanup", () => ({
+  registerManagerForCleanup: mock(() => {}),
+}))
+
+mock.module("./plugin-handlers", () => ({
+  createConfigHandler: mock(() => ({ kind: "config-handler" })),
+}))
+
+mock.module("./shared/tmux/tmux-utils/server-health", () => ({
+  isServerRunning: mock(async () => true),
+  markServerRunningInProcess,
+  resetServerCheck: mock(() => {}),
+}))
+
+const { createManagers } = await import("./create-managers")
+
+function createTmuxConfig(enabled: boolean) {
+  return {
+    enabled,
+    layout: "main-vertical" as const,
+    main_pane_size: 60,
+    main_pane_min_width: 120,
+    agent_pane_min_width: 40,
+    isolation: "inline" as const,
+  }
+}
+
+describe("createManagers", () => {
+  beforeEach(() => {
+    markServerRunningInProcess.mockClear()
+  })
+
+  afterAll(() => {
+    mock.restore()
+  })
+
+  it("#given tmux integration is disabled #when managers are created #then it does not mark the tmux server as running", () => {
+    // #given
+    const args = {
+      ctx: { directory: "/tmp", client: {} },
+      pluginConfig: {},
+      tmuxConfig: createTmuxConfig(false),
+      modelCacheState: {},
+      backgroundNotificationHookEnabled: false,
+    } as Parameters<typeof createManagers>[0]
+
+    // #when
+    createManagers(args)
+
+    // #then
+    expect(markServerRunningInProcess).not.toHaveBeenCalled()
+  })
+
+  it("#given tmux integration is enabled #when managers are created #then it marks the tmux server as running", () => {
+    // #given
+    const args = {
+      ctx: { directory: "/tmp", client: {} },
+      pluginConfig: {},
+      tmuxConfig: createTmuxConfig(true),
+      modelCacheState: {},
+      backgroundNotificationHookEnabled: false,
+    } as Parameters<typeof createManagers>[0]
+
+    // #when
+    createManagers(args)
+
+    // #then
+    expect(markServerRunningInProcess).toHaveBeenCalledTimes(1)
+  })
+})