arugyani_depends/tests/debounce.test.ts

import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
import { debounce } from "../src/debounce";

describe("debounce", () => {
  beforeEach(() => {
    vi.useFakeTimers();
  });
  afterEach(() => {
    vi.useRealTimers();
  });

  it("calls on the trailing edge after the delay", () => {
    const fn = vi.fn();
    const d = debounce(fn, 100);
    d();
    expect(fn).not.toHaveBeenCalled();
    vi.advanceTimersByTime(99);
    expect(fn).not.toHaveBeenCalled();
    vi.advanceTimersByTime(1);
    expect(fn).toHaveBeenCalledTimes(1);
  });

  it("coalesces rapid calls into a single trailing invocation", () => {
    const fn = vi.fn();
    const d = debounce(fn, 100);
    d(1);
    d(2);
    d(3);
    vi.advanceTimersByTime(100);
    expect(fn).toHaveBeenCalledTimes(1);
    expect(fn).toHaveBeenCalledWith(3);
  });

  it("resets the timer on each call", () => {
    const fn = vi.fn();
    const d = debounce(fn, 100);
    d();
    vi.advanceTimersByTime(80);
    d();
    vi.advanceTimersByTime(80);
    expect(fn).not.toHaveBeenCalled();
    vi.advanceTimersByTime(20);
    expect(fn).toHaveBeenCalledTimes(1);
  });

  it("cancel() prevents pending invocation", () => {
    const fn = vi.fn();
    const d = debounce(fn, 100);
    d();
    d.cancel();
    vi.advanceTimersByTime(200);
    expect(fn).not.toHaveBeenCalled();
  });

  it("flush() invokes immediately if pending", () => {
    const fn = vi.fn();
    const d = debounce(fn, 100);
    d("a");
    d.flush();
    expect(fn).toHaveBeenCalledWith("a");
    vi.advanceTimersByTime(200);
    expect(fn).toHaveBeenCalledTimes(1);
  });

  it("flush() is a no-op when nothing pending", () => {
    const fn = vi.fn();
    const d = debounce(fn, 100);
    d.flush();
    expect(fn).not.toHaveBeenCalled();
  });
});