Function toBeLeft

Example

import { left, right } from 'fp-ts/lib/Either'

test('passes when Either is a left', () => {
  const actual = left(Error())
  expect(actual).toBeLeft()
})

test('passes when Either is a right', () => {
  const actual = right({ test: 'ok' })
  expect(actual).not.toBeLeft()
})
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