diff --git a/src/hooks/auto-update-checker/hook.test.ts b/src/hooks/auto-update-checker/hook.test.ts
new file mode 100644
index 000000000..ecac1f8b1
--- /dev/null
+++ b/src/hooks/auto-update-checker/hook.test.ts
@@ -0,0 +1,87 @@
+import type { PluginInput } from "@opencode-ai/plugin"
+import { describe, expect, mock, test } from "bun:test"
+
+const latestVersionMock = mock.fn(async () => "3.0.1")
+const scheduleDeferredIdleCheckMock = mock.fn((runCheck: () => void) => {
+  scheduledCheck = runCheck
+})
+
+let scheduledCheck: (() => void) | null = null
+
+mock.module("./checker/latest-version", () => ({
+  getLatestVersion: latestVersionMock,
+}))
+
+mock.module("./hook/deferred-idle-check", () => ({
+  scheduleDeferredIdleCheck: scheduleDeferredIdleCheckMock,
+}))
+
+const createHook = async () => {
+  const module = await import("./hook")
+  return module.createAutoUpdateCheckerHook(
+    {
+      directory: "/tmp/project",
+      client: {
+        tui: {
+          showToast: async () => undefined,
+        },
+      },
+    } satisfies PluginInput,
+    {
+      showStartupToast: false,
+      autoUpdate: false,
+    },
+    {
+      getCachedVersion: () => "3.0.0",
+      getLocalDevVersion: () => null,
+      showConfigErrorsIfAny: async () => undefined,
+      updateAndShowConnectedProvidersCacheStatus: async () => undefined,
+      refreshModelCapabilitiesOnStartup: async () => undefined,
+      showModelCacheWarningIfNeeded: async () => undefined,
+      showLocalDevToast: async () => undefined,
+      showVersionToast: async () => undefined,
+      runBackgroundUpdateCheck: async () => {
+        await latestVersionMock()
+      },
+      log: () => undefined,
+    },
+  )
+}
+
+describe("auto-update-checker hook", () => {
+  test("defers update check until first session idle", async () => {
+    // given
+    latestVersionMock.mockClear()
+    scheduleDeferredIdleCheckMock.mockClear()
+    scheduledCheck = null
+    const hook = await createHook()
+
+    // when
+    hook.event({ event: { type: "session.created" } })
+
+    // then
+    expect(scheduleDeferredIdleCheckMock).toHaveBeenCalledTimes(0)
+    expect(latestVersionMock).toHaveBeenCalledTimes(0)
+
+    // when
+    hook.event({ event: { type: "session.idle" } })
+
+    // then
+    expect(scheduleDeferredIdleCheckMock).toHaveBeenCalledTimes(1)
+    expect(latestVersionMock).toHaveBeenCalledTimes(0)
+
+    // when
+    scheduledCheck?.()
+
+    // then
+    expect(latestVersionMock).toHaveBeenCalledTimes(1)
+
+    // when
+    hook.event({ event: { type: "session.idle" } })
+    scheduledCheck?.()
+
+    // then
+    expect(scheduleDeferredIdleCheckMock).toHaveBeenCalledTimes(1)
+    expect(latestVersionMock).toHaveBeenCalledTimes(1)
+  })
+})