How to write your own test cases and test

authorYourOwnUnitTests.js

/*
You are given an array `numbers` and an integer `pivot`

Your task is to return a new array in with the i-th element equals:
    - 0 if numbers[i] is zero
    - 1 if numbers[i] and the pivot have the same sign
    - -1 if the numbers[i] and the pivot have differing signs
*/
function assessNums(nums, pivot) {
  const output = []
  nums.forEach(num => {
    if (num === 0) {
      output.push(0)
    } else if ((num < 0 && pivot < 0) || (num >= 0 && pivot >= 0))  {
      output.push(1)
    } else { // differing signs
      output.push(-1)
    }
  })
  return output;
}

const testCases = [
  {
    args: [ [6, -5, 0], 2 ],
    expected: [1, -1, 1]
  },

  {
    args: [[5, -4, 0, -3, 2], -5],
    expected: [-1, 1, 0, 1, 1]
  },

  // third test case and expected result, etc
]

testCases.forEach((testCase, idx) => {
  // destructuring assignment
  [numbers, pivot] = testCase.args;
  const got = assessNums(numbers, pivot);
  // NOTE: must use `JSON.stringify` to do array equality checks
  if (JSON.stringify(got) != JSON.stringify(testCase.expected)) {
    const errorMsg = [
      `test case ${idx + 1} FAILED`,
      '-----',
      `GOT:\n\t${got}`,
      '\n',
      `EXPECTED:\n\t${testCase.expected}`,
      '\n\n'
    ]
    console.error(errorMsg.join('\n'));
  }
})