fix(virtual-core): fix total size calculation for single item in multi-lane

[greenblues1190]

This is a follow-up to #961. The original issue still occurs when there's only one item in a multi-lane layout.

This PR changes the loop condition in getTotalSize() to handle cases where only one item exists in multi-lane. The previous condition skipped the loop when endIndex === 0, which caused the total size to be incorrectly calculated as 0.

I used the following test to verify the fix locally:

test("should return correct total size with single item in multi-lane", () => {
  const virtualizer = new Virtualizer({
    count: 1,
    lanes: 2,
    getScrollElement: () => null,
    estimateSize: () => 50,
    scrollToFn: vi.fn(),
    observeElementRect: vi.fn(),
    observeElementOffset: vi.fn(),
  });
  expect(virtualizer.getTotalSize()).toBe(50);
});

This is a fairly specific edge case, so I didn’t include the test in the commit.
Happy to add it if you think it’d be useful to include in the suite!

Fixes #963

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[piecyk]

Thanks, @greenblues1190! Let's add the test. Overall, the tests need some attention. The plan is to refactor the current unit tests a bit and add browser testing using Playwright.

[soren121]

If this is an off-by-one, then the condition on L1165 also needs to be adjusted (it's essentially the same loop.)

[greenblues1190]

@piecyk Test added!

@soren121 You're right, I’ve updated the condition too.

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☁️ Nx Cloud last updated this comment at 2025-03-31 06:28:27 UTC

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