tests(solid-virtual): add reactivity tests

Author: gameroman

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

@@ -0,0 +1,44 @@
+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()
+    })
+  })
+})