diff --git a/src/commands/status.update.test.ts b/src/commands/status.update.test.ts
new file mode 100644
index 00000000000..8f3f4e3aff4
--- /dev/null
+++ b/src/commands/status.update.test.ts
@@ -0,0 +1,108 @@
+import { describe, expect, it } from "vitest";
+import type { UpdateCheckResult } from "../infra/update-check.js";
+import { VERSION } from "../version.js";
+import { formatUpdateOneLiner, resolveUpdateAvailability } from "./status.update.js";
+
+function buildUpdate(partial: Partial<UpdateCheckResult>): UpdateCheckResult {
+  return {
+    root: null,
+    installKind: "unknown",
+    packageManager: "unknown",
+    ...partial,
+  };
+}
+
+function nextMajorVersion(version: string): string {
+  const [majorPart] = version.split(".");
+  const major = Number.parseInt(majorPart ?? "", 10);
+  if (Number.isFinite(major) && major >= 0) {
+    return `${major + 1}.0.0`;
+  }
+  return "999999.0.0";
+}
+
+describe("resolveUpdateAvailability", () => {
+  it("flags git update when behind upstream", () => {
+    const update = buildUpdate({
+      installKind: "git",
+      git: {
+        root: "/tmp/repo",
+        sha: null,
+        tag: null,
+        branch: "main",
+        upstream: "origin/main",
+        dirty: false,
+        ahead: 0,
+        behind: 3,
+        fetchOk: true,
+      },
+    });
+    expect(resolveUpdateAvailability(update)).toEqual({
+      available: true,
+      hasGitUpdate: true,
+      hasRegistryUpdate: false,
+      latestVersion: null,
+      gitBehind: 3,
+    });
+  });
+
+  it("flags registry update when latest version is newer", () => {
+    const latestVersion = nextMajorVersion(VERSION);
+    const update = buildUpdate({
+      installKind: "package",
+      packageManager: "pnpm",
+      registry: { latestVersion },
+    });
+    const availability = resolveUpdateAvailability(update);
+    expect(availability.available).toBe(true);
+    expect(availability.hasGitUpdate).toBe(false);
+    expect(availability.hasRegistryUpdate).toBe(true);
+    expect(availability.latestVersion).toBe(latestVersion);
+  });
+});
+
+describe("formatUpdateOneLiner", () => {
+  it("renders git status and registry latest summary", () => {
+    const update = buildUpdate({
+      installKind: "git",
+      git: {
+        root: "/tmp/repo",
+        sha: "abc123456789",
+        tag: null,
+        branch: "main",
+        upstream: "origin/main",
+        dirty: true,
+        ahead: 0,
+        behind: 2,
+        fetchOk: true,
+      },
+      registry: { latestVersion: VERSION },
+      deps: {
+        manager: "pnpm",
+        status: "ok",
+        lockfilePath: "pnpm-lock.yaml",
+        markerPath: "node_modules/.modules.yaml",
+      },
+    });
+
+    expect(formatUpdateOneLiner(update)).toBe(
+      `Update: git main · ↔ origin/main · dirty · behind 2 · npm latest ${VERSION} · deps ok`,
+    );
+  });
+
+  it("renders package-manager mode with registry error", () => {
+    const update = buildUpdate({
+      installKind: "package",
+      packageManager: "npm",
+      registry: { latestVersion: null, error: "offline" },
+      deps: {
+        manager: "npm",
+        status: "missing",
+        lockfilePath: "package-lock.json",
+        markerPath: "node_modules",
+      },
+    });
+
+    expect(formatUpdateOneLiner(update)).toBe("Update: npm · npm latest unknown · deps missing");
+  });
+});
diff --git a/src/logging/timestamps.test.ts b/src/logging/timestamps.test.ts
new file mode 100644
index 00000000000..f2d72125987
--- /dev/null
+++ b/src/logging/timestamps.test.ts
@@ -0,0 +1,58 @@
+import { describe, expect, it } from "vitest";
+import { formatLocalIsoWithOffset } from "./timestamps.js";
+
+function buildFakeDate(parts: {
+  year: number;
+  month: number;
+  day: number;
+  hour: number;
+  minute: number;
+  second: number;
+  millisecond: number;
+  timezoneOffsetMinutes: number;
+}): Date {
+  return {
+    getFullYear: () => parts.year,
+    getMonth: () => parts.month - 1,
+    getDate: () => parts.day,
+    getHours: () => parts.hour,
+    getMinutes: () => parts.minute,
+    getSeconds: () => parts.second,
+    getMilliseconds: () => parts.millisecond,
+    getTimezoneOffset: () => parts.timezoneOffsetMinutes,
+  } as unknown as Date;
+}
+
+describe("formatLocalIsoWithOffset", () => {
+  it("formats positive offset with millisecond padding", () => {
+    const value = formatLocalIsoWithOffset(
+      buildFakeDate({
+        year: 2026,
+        month: 1,
+        day: 2,
+        hour: 3,
+        minute: 4,
+        second: 5,
+        millisecond: 6,
+        timezoneOffsetMinutes: -150, // UTC+02:30
+      }),
+    );
+    expect(value).toBe("2026-01-02T03:04:05.006+02:30");
+  });
+
+  it("formats negative offset", () => {
+    const value = formatLocalIsoWithOffset(
+      buildFakeDate({
+        year: 2026,
+        month: 12,
+        day: 31,
+        hour: 23,
+        minute: 59,
+        second: 58,
+        millisecond: 321,
+        timezoneOffsetMinutes: 300, // UTC-05:00
+      }),
+    );
+    expect(value).toBe("2026-12-31T23:59:58.321-05:00");
+  });
+});