How to use jest.each

Pass data as array:

function hasDuplicates(arr: any[]) {
  return new Set(arr).size !== arr.length
}

describe('hasDuplicates', () => {
  test.each([
    [[2, 4, 4, 6], true],
    [[2, 4, 6, 1, 6], true],
  ])(
    'returns true if array has duplicates (e.g., %s)',
    (input, expectedResult) => {
      expect(hasDuplicates(input)).toEqual(expectedResult)
    }
  )

  test.each([
    [[2, 4, 6], false],
    [[2, 4, 6, 1, 5], false],
  ])(
    "returns false if array doesn't have duplicates (e.g., %s)",
    (input, expectedResult) => {
      expect(hasDuplicates(input)).toEqual(expectedResult)
    }
  )
})

Pass data as object:

test.each([
  {a: 1, b: 1, expected: 2},
  {a: 1, b: 2, expected: 3},
  {a: 2, b: 1, expected: 3},
])('.add($a, $b)', ({a, b, expected}) => {
  expect(a + b).toBe(expected);
});

Sources

• jest.each – Jest docs