getUpdatedOffsetForIndex.jest.js

import getUpdatedOffsetForIndex from './getUpdatedOffsetForIndex';
import {getCellMetadata} from './TestHelper';

describe('getUpdatedOffsetForIndex', () => {
  function testHelper(
    targetIndex,
    currentOffset,
    cellMetadata = getCellMetadata(),
  ) {
    return getUpdatedOffsetForIndex({
      cellOffset: cellMetadata[targetIndex].offset,
      cellSize: cellMetadata[targetIndex].size,
      containerSize: 50,
      currentOffset,
    });
  }

  it('should scroll to the beginning', () => {
    expect(testHelper(0, 100)).toEqual(0);
  });

  it('should scroll forward to the middle', () => {
    expect(testHelper(4, 0)).toEqual(20);
  });

  it('should scroll backward to the middle', () => {
    expect(testHelper(2, 100)).toEqual(30);
  });

  it('should not scroll if an item is already visible', () => {
    expect(testHelper(2, 20)).toEqual(20);
  });

  it('should scroll to the end', () => {
    expect(testHelper(8, 0)).toEqual(110);
  });

  it('should honor specified :align values', () => {
    expect(
      getUpdatedOffsetForIndex({
        align: 'auto',
        cellOffset: 50,
        cellSize: 10,
        containerSize: 50,
        currentOffset: 0,
      }),
    ).toEqual(10);
    expect(
      getUpdatedOffsetForIndex({
        align: 'start',
        cellOffset: 50,
        cellSize: 10,
        containerSize: 50,
        currentOffset: 0,
      }),
    ).toEqual(50);
    expect(
      getUpdatedOffsetForIndex({
        align: 'auto',
        cellOffset: 50,
        cellSize: 10,
        containerSize: 50,
        currentOffset: 100,
      }),
    ).toEqual(50);
    expect(
      getUpdatedOffsetForIndex({
        align: 'end',
        cellOffset: 50,
        cellSize: 10,
        containerSize: 50,
        currentOffset: 100,
      }),
    ).toEqual(10);
    expect(
      getUpdatedOffsetForIndex({
        align: 'center',
        cellOffset: 50,
        cellSize: 10,
        containerSize: 50,
        currentOffset: 100,
      }),
    ).toEqual(30);
  });
});