test: add solid-virtual tests

packages/solid-virtual/tests/filter-items.test.ts

@@ -0,0 +1,51 @@
+import { expect, test } from 'vitest'
+import { createRoot, createSignal } from 'solid-js'
+
+import { createVirtualizer } from '../src/index'
+
+test('virtual items correctly index into filtered data after reactive shrink', () => {
+  createRoot((dispose) => {
+    const all = ['apple', 'banana', 'cherry', 'date', 'fig', 'grape']
+    const [query, setQuery] = createSignal('')
+
+    const filtered = () => {
+      const q = query()
+      if (!q) return all
+      return all.filter(s => s.includes(q))
+    }
+
+    const virtualizer = createVirtualizer<HTMLDivElement, HTMLDivElement>({
+      get count() {
+        return filtered().length
+      },
+      getScrollElement: () => null,
+      estimateSize: () => 60,
+      initialRect: { width: 800, height: 600 },
+    })
+
+    expect(virtualizer.getVirtualItems().length).toBe(6)
+    expect(virtualizer.getVirtualItems().map(v => filtered()[v.index]))
+      .toEqual(['apple', 'banana', 'cherry', 'date', 'fig', 'grape'])
+
+    setQuery('e')
+
+    expect(virtualizer.getVirtualItems().length).toBe(4)
+    const items = virtualizer.getVirtualItems()
+    expect(items.map(v => filtered()[v.index]))
+      .toEqual(['apple', 'cherry', 'date', 'grape'])
+
+    setQuery('zz')
+
+    expect(virtualizer.getVirtualItems().length).toBe(0)
+    expect(virtualizer.getVirtualItems().map(v => filtered()[v.index]))
+      .toEqual([])
+
+    setQuery('cherry')
+
+    expect(virtualizer.getVirtualItems().length).toBe(1)
+    expect(virtualizer.getVirtualItems().map(v => filtered()[v.index]))
+      .toEqual(['cherry'])
+
+    dispose()
+  })
+})

packages/solid-virtual/tests/reactivity.test.ts

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+import { describe, expect, it } from 'vitest'
+import { createRoot, createSignal } from 'solid-js'
+import { unwrap } from 'solid-js/store'
+import { createVirtualizer } from '../src/index'
+
+describe('reactivity: unaffected slots keep stable references', () => {
+  it('does not recreate VirtualItem objects for slots whose data did not change', () => {
+    createRoot((dispose) => {
+      const data = Array.from({ length: 50 }, (_, i) => `item-${i}`)
+      const [filtered, setFiltered] = createSignal(data)
+
+      const virtualizer = createVirtualizer({
+        get count() {
+          return filtered().length
+        },
+        getScrollElement: () => document.createElement('div'),
+        estimateSize: () => 30,
+        overscan: 0,
+      })
+
+      const before = virtualizer.getVirtualItems()
+      const beforeRefs = before.map((item) => unwrap(item))
+
+      // Shrink the array; leaves the first visible rows' index/start/end/size untouched.
+      setFiltered(data.slice(0, 40))
+
+      const after = virtualizer.getVirtualItems()
+      const afterRefs = after.map((item) => unwrap(item))
+
+      const unaffectedCount = Math.min(beforeRefs.length, afterRefs.length)
+      for (let i = 0; i < unaffectedCount; i++) {
+        if (
+          beforeRefs[i].start === afterRefs[i].start &&
+          beforeRefs[i].end === afterRefs[i].end &&
+          beforeRefs[i].index === afterRefs[i].index
+        ) {
+          expect(afterRefs[i]).toBe(beforeRefs[i])
+        }
+      }
+
+      dispose()
+    })
+  })
+})