test: add branch coverage for formatter and useUpdater edge cases (#1201)

- formatBytes: test negative decimals clamped to 0 (decimals<0 branch)
- formatDuration: test zero-hours/minutes cases and days-only durations
  (uncovered ternary branches on the template-literal return line)
- useUpdater: test percent=null when total===0n (BigInt zero-guard branch)
- useUpdater: test install() when contentLength is absent (total stays null)
- useUpdater: test fetchUpdate error path (meta stays null on non-ok result)

formatter.ts branches: 82.35% → 100%
useAppUpdate.ts branches: 76.92% → 92.3%

Co-authored-by: Test Improver <copilot-test-improver@github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: shm <m11c3.sh@gmail.com>

Author: 4 people

src/features/updater/hooks/useAppUpdate.test.ts

@@ -120,4 +120,65 @@ describe("useUpdater", () => {
     expect(result.current.total).toBeNull();
     expect(result.current.percent).toBeNull();
   });
+
+  it("percent: null when total is 0n", async () => {
+    // Edge case: started event sends contentLength "0", total becomes 0n
+    (commands.installUpdate as Mock).mockImplementation(async (ch: unknown) => {
+      const channel = ch as TestChannel;
+      channel.onmessage?.({ event: "started", data: { contentLength: "0" } });
+      channel.onmessage?.({ event: "finished", data: {} });
+      return { status: "ok", data: null };
+    });
+
+    const { result } = renderHook(() => useUpdater());
+
+    await act(async () => {
+      await result.current.install();
+    });
+
+    await waitFor(() => result.current.isFinished === true);
+    // total is 0n, so percent must be null (division by zero guard)
+    expect(result.current.percent).toBeNull();
+  });
+
+  it("install: total stays null when contentLength is absent", async () => {
+    // started event without contentLength → setTotal(null)
+    (commands.installUpdate as Mock).mockImplementation(async (ch: unknown) => {
+      const channel = ch as TestChannel;
+      channel.onmessage?.({
+        event: "started",
+        // contentLength omitted → falsy
+        data: { contentLength: "" },
+      });
+      channel.onmessage?.({ event: "progress", data: { chunkLength: "50" } });
+      channel.onmessage?.({ event: "finished", data: {} });
+      return { status: "ok", data: null };
+    });
+
+    const { result } = renderHook(() => useUpdater());
+
+    await act(async () => {
+      await result.current.install();
+    });
+
+    await waitFor(() => result.current.isFinished === true);
+    // total should remain null (unknown download size)
+    expect(result.current.total).toBeNull();
+    expect(result.current.percent).toBeNull();
+  });
+
+  it("fetchUpdate: meta stays null when result is not ok", async () => {
+    (commands.fetchUpdate as Mock).mockResolvedValue({
+      status: "error",
+      error: "network failure",
+    });
+
+    const { result } = renderHook(() => useUpdater());
+
+    await act(async () => {
+      await new Promise((resolve) => setTimeout(resolve, 50));
+    });
+
+    expect(result.current.meta).toBeNull();
+  });
 });

src/lib/formatter.test.ts

@@ -16,6 +16,13 @@ describe("formatBytes", () => {
     expect(formatBytes(1024 ** 2)).toEqual([1, "MB"]);
     expect(formatBytes(1024 ** 3)).toEqual([1, "GB"]);
   });
+
+  it("should clamp negative decimals to 0", () => {
+    // decimals < 0 branch: should behave as decimals = 0
+    const [value] = formatBytes(1024, -1);
+    expect(Number.isInteger(value)).toBe(true);
+    expect(value).toBe(1);
+  });
 });
 
 describe("formatDuration", () => {
@@ -26,6 +33,21 @@ describe("formatDuration", () => {
   it("should format duration in Japanese", () => {
     expect(formatDuration(90061, "ja-JP")).toBe("1日 1時間 1分 1秒");
   });
+
+  it("should omit zero hours and minutes", () => {
+    // h = 0, m = 0 — only seconds
+    expect(formatDuration(45, "en-US")).toBe("45second");
+  });
+
+  it("should omit zero hours when only minutes and seconds", () => {
+    // h = 0, m > 0
+    expect(formatDuration(125, "en-US")).toBe("2minute 5second");
+  });
+
+  it("should format days without hours in English", () => {
+    // d > 0, h = 0, m = 0
+    expect(formatDuration(86400, "en-US")).toBe("1day 0second");
+  });
 });
 
 describe("formatBytesBigint", () => {