@@ -0,0 +1,337 @@
+import { expect, test, vi } from 'vitest'
+import {
+  Virtualizer,
+  elementScroll,
+  observeElementOffset,
+  observeElementRect,
+  observeWindowOffset,
+  windowScroll,
+} from '../src/index'
+
+// ─── elementScroll / windowScroll public exports ─────────────────────────────
+
+function makeBaseInstance(scrollEl: any, opts: any = {}) {
+  return {
+    scrollElement: scrollEl,
+    options: {
+      horizontal: false,
+      ...opts,
+    },
+  } as any
+}
+
+test('elementScroll: calls scrollTo with top + behavior on the scroll element', () => {
+  const scrollTo = vi.fn()
+  const scrollEl = { scrollTo }
+  elementScroll(100, { behavior: 'smooth' }, makeBaseInstance(scrollEl) as any)
+  expect(scrollTo).toHaveBeenCalledWith({ top: 100, behavior: 'smooth' })
+})
+
+test('elementScroll: applies adjustments offset', () => {
+  const scrollTo = vi.fn()
+  const scrollEl = { scrollTo }
+  elementScroll(
+    100,
+    { adjustments: 50, behavior: 'auto' },
+    makeBaseInstance(scrollEl) as any,
+  )
+  expect(scrollTo).toHaveBeenCalledWith({ top: 150, behavior: 'auto' })
+})
+
+test('elementScroll: uses left when horizontal is true', () => {
+  const scrollTo = vi.fn()
+  const scrollEl = { scrollTo }
+  elementScroll(
+    100,
+    { behavior: 'auto' },
+    makeBaseInstance(scrollEl, { horizontal: true }) as any,
+  )
+  expect(scrollTo).toHaveBeenCalledWith({ left: 100, behavior: 'auto' })
+})
+
+test('windowScroll: calls scrollTo with top + behavior on the window', () => {
+  const scrollTo = vi.fn()
+  const win = { scrollTo }
+  windowScroll(250, { behavior: 'smooth' }, makeBaseInstance(win) as any)
+  expect(scrollTo).toHaveBeenCalledWith({ top: 250, behavior: 'smooth' })
+})
+
+test('windowScroll: applies adjustments + horizontal', () => {
+  const scrollTo = vi.fn()
+  const win = { scrollTo }
+  windowScroll(
+    250,
+    { adjustments: -10, behavior: 'auto' },
+    makeBaseInstance(win, { horizontal: true }) as any,
+  )
+  expect(scrollTo).toHaveBeenCalledWith({ left: 240, behavior: 'auto' })
+})
+
+test('elementScroll / windowScroll: no-op when scrollElement is null', () => {
+  expect(() =>
+    elementScroll(100, {}, makeBaseInstance(null) as any),
+  ).not.toThrow()
+  expect(() =>
+    windowScroll(100, {}, makeBaseInstance(null) as any),
+  ).not.toThrow()
+})
+
+// ─── observeElementOffset / observeWindowOffset ──────────────────────────────
+
+function makeObserveInstance(
+  element: any,
+  opts: {
+    horizontal?: boolean
+    isRtl?: boolean
+    useScrollendEvent?: boolean
+    isScrollingResetDelay?: number
+  } = {},
+  targetWindow: any = {
+    setTimeout: globalThis.setTimeout.bind(globalThis),
+    clearTimeout: globalThis.clearTimeout.bind(globalThis),
+  },
+) {
+  return {
+    scrollElement: element,
+    targetWindow,
+    options: {
+      horizontal: false,
+      isRtl: false,
+      useScrollendEvent: false,
+      isScrollingResetDelay: 150,
+      ...opts,
+    },
+  } as any
+}
+
+test('observeElementOffset: returns undefined when scrollElement is null', () => {
+  const cb = vi.fn()
+  expect(
+    observeElementOffset(makeObserveInstance(null) as any, cb),
+  ).toBeUndefined()
+  expect(cb).not.toHaveBeenCalled()
+})
+
+test('observeElementOffset: attaches scroll listener and fires callback with scrollTop', () => {
+  const cb = vi.fn()
+  const listeners = new Map<string, EventListener>()
+  const el: any = {
+    scrollTop: 50,
+    scrollLeft: 0,
+    addEventListener: (name: string, fn: any) => listeners.set(name, fn),
+    removeEventListener: (name: string) => listeners.delete(name),
+  }
+  const cleanup = observeElementOffset(makeObserveInstance(el) as any, cb)
+  expect(listeners.has('scroll')).toBe(true)
+  // No scrollend listener by default
+  expect(listeners.has('scrollend')).toBe(false)
+  // Trigger scroll
+  listeners.get('scroll')!({} as Event)
+  expect(cb).toHaveBeenCalledWith(50, true)
+  cleanup?.()
+  expect(listeners.has('scroll')).toBe(false)
+})
+
+test('observeElementOffset: fallback reads offset after programmatic changes', () => {
+  vi.useFakeTimers()
+  try {
+    const cb = vi.fn()
+    const listeners = new Map<string, EventListener>()
+    const el: any = {
+      scrollTop: 50,
+      scrollLeft: 0,
+      addEventListener: (name: string, fn: any) => listeners.set(name, fn),
+      removeEventListener: (name: string) => listeners.delete(name),
+    }
+    observeElementOffset(makeObserveInstance(el) as any, cb)
+
+    listeners.get('scroll')!({} as Event)
+    el.scrollTop = 125
+    vi.advanceTimersByTime(150)
+
+    expect(cb).toHaveBeenLastCalledWith(125, false)
+  } finally {
+    vi.useRealTimers()
+  }
+})
+
+// ─── cleanup resets the scroll flags ─────────────────────────────────────────
+// The cancelled debounce is the only writer of `isScrolling = false`, and
+// `cleanup()` also runs while the instance stays alive (element swap,
+// `enabled: false`), so it has to reset the flags itself.
+
+const makeScrollFlagsVirtualizer = () => {
+  const MockResizeObserver = vi.fn(function () {
+    return { observe: vi.fn(), unobserve: vi.fn(), disconnect: vi.fn() }
+  })
+  const mockWindow = {
+    requestAnimationFrame: vi.fn(),
+    cancelAnimationFrame: vi.fn(),
+    ResizeObserver: MockResizeObserver,
+  }
+  const makeElement = () =>
+    ({
+      scrollTop: 0,
+      scrollLeft: 0,
+      scrollWidth: 1000,
+      scrollHeight: 5000,
+      offsetWidth: 400,
+      offsetHeight: 600,
+      ownerDocument: { defaultView: mockWindow },
+    }) as unknown as HTMLDivElement
+
+  const first = makeElement()
+  const second = makeElement()
+  let element: HTMLDivElement | null = first
+  let emit: ((offset: number, isScrolling: boolean) => void) | null = null
+
+  const virtualizer = new Virtualizer({
+    count: 100,
+    estimateSize: () => 50,
+    getScrollElement: () => element,
+    scrollToFn: vi.fn(),
+    observeElementRect: (_instance, cb) => {
+      cb({ width: 400, height: 600 })
+      return () => {}
+    },
+    observeElementOffset: (_instance, cb) => {
+      emit = cb
+      return () => {}
+    },
+  })
+
+  virtualizer._willUpdate()
+
+  // Mid-scroll: this is the state the debounce used to clear on its own.
+  emit!(500, true)
+
+  return {
+    virtualizer,
+    swapElement: () => {
+      element = second
+      virtualizer._willUpdate()
+    },
+    disable: () => {
+      element = null
+      virtualizer._willUpdate()
+    },
+  }
+}
+
+test('cleanup resets the scroll flags when the scroll element is swapped', () => {
+  const { virtualizer, swapElement } = makeScrollFlagsVirtualizer()
+
+  expect(virtualizer.isScrolling).toBe(true)
+
+  swapElement()
+
+  expect(virtualizer.isScrolling).toBe(false)
+  expect(virtualizer.scrollDirection).toBe(null)
+})
+
+test('cleanup resets the scroll flags when the scroll element goes away', () => {
+  const { virtualizer, disable } = makeScrollFlagsVirtualizer()
+
+  expect(virtualizer.isScrolling).toBe(true)
+
+  disable()
+
+  expect(virtualizer.isScrolling).toBe(false)
+  expect(virtualizer.scrollDirection).toBe(null)
+})
+
+test('cleanup resets the scroll flags on unmount', () => {
+  const { virtualizer } = makeScrollFlagsVirtualizer()
+
+  expect(virtualizer.isScrolling).toBe(true)
+
+  virtualizer._didMount()()
+
+  expect(virtualizer.isScrolling).toBe(false)
+  expect(virtualizer.scrollDirection).toBe(null)
+})
+
+test('observeElementOffset: cleanup drops the queued isScrolling reset', () => {
+  vi.useFakeTimers()
+  try {
+    const cb = vi.fn()
+    const listeners = new Map<string, EventListener>()
+    const el: any = {
+      scrollTop: 50,
+      scrollLeft: 0,
+      addEventListener: (name: string, fn: any) => listeners.set(name, fn),
+      removeEventListener: (name: string) => listeners.delete(name),
+    }
+    const cleanup = observeElementOffset(makeObserveInstance(el) as any, cb)
+
+    // Each scroll arms a debounce that resets isScrolling to false.
+    listeners.get('scroll')!({} as Event)
+    expect(cb).toHaveBeenCalledWith(50, true)
+    cb.mockClear()
+
+    // Tearing down inside that window must not leave the reset queued —
+    // it would arrive after the consumer stopped listening.
+    cleanup?.()
+    vi.advanceTimersByTime(1000)
+
+    expect(cb).not.toHaveBeenCalled()
+  } finally {
+    vi.useRealTimers()
+  }
+})
+
+test('observeElementOffset: reads scrollLeft + applies isRtl when horizontal', () => {
+  const cb = vi.fn()
+  const listeners = new Map<string, EventListener>()
+  const el: any = {
+    scrollTop: 0,
+    scrollLeft: 80,
+    addEventListener: (name: string, fn: any) => listeners.set(name, fn),
+    removeEventListener: (name: string) => listeners.delete(name),
+  }
+  observeElementOffset(
+    makeObserveInstance(el, { horizontal: true, isRtl: true }) as any,
+    cb,
+  )
+  listeners.get('scroll')!({} as Event)
+  // isRtl flips sign
+  expect(cb).toHaveBeenCalledWith(-80, true)
+})
+
+test('observeWindowOffset: returns undefined when scrollElement is null', () => {
+  const cb = vi.fn()
+  expect(
+    observeWindowOffset(makeObserveInstance(null) as any, cb),
+  ).toBeUndefined()
+})
+
+test('observeWindowOffset: attaches scroll listener and fires callback with scrollY', () => {
+  const cb = vi.fn()
+  const listeners = new Map<string, EventListener>()
+  const win: any = {
+    scrollX: 0,
+    scrollY: 120,
+    addEventListener: (name: string, fn: any) => listeners.set(name, fn),
+    removeEventListener: (name: string) => listeners.delete(name),
+  }
+  const cleanup = observeWindowOffset(makeObserveInstance(win) as any, cb)
+  expect(listeners.has('scroll')).toBe(true)
+  listeners.get('scroll')!({} as Event)
+  expect(cb).toHaveBeenCalledWith(120, true)
+  cleanup?.()
+  expect(listeners.has('scroll')).toBe(false)
+})
+
+test('observeWindowOffset: reads scrollX when horizontal', () => {
+  const cb = vi.fn()
+  const listeners = new Map<string, EventListener>()
+  const win: any = {
+    scrollX: 75,
+    scrollY: 0,
+    addEventListener: (name: string, fn: any) => listeners.set(name, fn),
+    removeEventListener: (name: string) => listeners.delete(name),
+  }
+  observeWindowOffset(makeObserveInstance(win, { horizontal: true }) as any, cb)
+  listeners.get('scroll')!({} as Event)
+  expect(cb).toHaveBeenCalledWith(75, true)
+})