src/core/either.spec.ts

import { Either, right, left } from '@/core/either';

function doSomething(shouldSuccess: boolean): Either<string, number> {
  if (shouldSuccess) {
    return right(10);
  }

  return left('error');
}

test('success result', () => {
  const successResult = doSomething(true);

  expect(successResult.isRight()).toBe(true);
});

test('error result', () => {
  const errorResult = doSomething(false);

  expect(errorResult.isLeft()).toBe(true);
});