Fixed topOffset and added tests (deephaven#2065)

packages/components/src/spectrum/utils/useStaticItemInitialScrollPosition.test.tsx

@@ -0,0 +1,57 @@
+import React from 'react';
+import { renderHook } from '@testing-library/react-hooks';
+import { Item, Section } from '../shared';
+import { ItemElement } from './itemUtils';
+import { useStaticItemInitialScrollPosition } from './useStaticItemInitialScrollPosition';
+
+beforeEach(() => {
+  jest.clearAllMocks();
+});
+
+afterEach(() => {
+  expect.hasAssertions();
+});
+
+const mockSelectedKey = 'selected.key';
+
+describe('useStaticItemInitialScrollPosition: selectedKey: %s', () => {
+  const itemHeight = 32;
+  const topOffset = 20;
+
+  const items = {
+    empty: [],
+    mixed: [<Item key="">Item</Item>, <Section key="">Test</Section>],
+    only: [
+      <Item key="a">Item</Item>,
+      <Item key="b">Item</Item>,
+      <Item key="c">Item</Item>,
+      <Item key={mockSelectedKey}>Item</Item>,
+      <Item key="e">Item</Item>,
+    ],
+  } satisfies Record<string, ItemElement<unknown>[]>;
+
+  it.each([
+    [items.empty, undefined, topOffset],
+    [items.mixed, undefined, topOffset],
+    [items.only, undefined, topOffset],
+    [items.empty, mockSelectedKey, topOffset],
+    [items.mixed, mockSelectedKey, topOffset],
+    [items.only, mockSelectedKey, topOffset + 3 * itemHeight],
+  ])(
+    'should return a function that returns the initial scroll position for item only collections: %s, %s',
+    async (givenItems, selectedKey, expected) => {
+      const { result } = renderHook(() =>
+        useStaticItemInitialScrollPosition({
+          itemHeight,
+          selectedKey,
+          topOffset,
+          items: givenItems,
+        })
+      );
+
+      const actual = await result.current();
+
+      expect(actual).toEqual(expected);
+    }
+  );
+});

packages/components/src/spectrum/utils/useStaticItemInitialScrollPosition.ts

@@ -35,7 +35,7 @@ export function useStaticItemInitialScrollPosition({
   const getInitialScrollPosition = useCallback(
     async () =>
       disableScrollOnOpen
-        ? null
+        ? topOffset
         : getPositionOfSelectedItemElement({
             items,
             itemHeight,