import expect from 'expect';
import deepfreeze from 'deepfreeze';

const addCounter = (list) => {
  return [...list, 0];
};

const removeCounter = (list, index) => {
  return [
    ...list.slice(0, index),
    ...list.slice(index + 1)
  ];
};

const incrementCounter = (list, index) => {
  return [
    ...list.slice(0, index),
    list[index] + 1,
    ...list.slice(index + 1)
  ];
};

const testAddCounter = () => {
  const listBefore = [];
  const listAfter = [0];

  deepfreeze(listBefore);

  expect(
    addCounter(listBefore)
  ).toEqual(listAfter);
};

const testRemoveCounter = () => {
  const listBefore = [0, 10, 20];
  const listAfter = [0, 20];

  deepfreeze(listBefore);

  expect(
    removeCounter(listBefore, 1)
  ).toEqual(listAfter);
};

const testIncrementCounter = () => {
  const listBefore = [0, 10, 20];
  const listAfter = [0, 11, 20];

  deepfreeze(listBefore);

  expect(
    incrementCounter(listBefore, 1)
  ).toEqual(listAfter);
};

testAddCounter();
testRemoveCounter();
testIncrementCounter();
console.log('All Tests Passed.')