DEV#175.js

// https://dev.to/thepracticaldev/daily-challenge-174-soccer-league-table-2393

function DNA_strand (str) {
  let result = ''
  for (let i = 0; i < str.length; i++) {
    switch (str[i]) {
      case 'A':
        result = result + 'T'
        break
      case 'T':
        result = result + 'A'
        break
      case 'C':
        result = result + 'G'
        break
      case 'G':
        result = result + 'C'
        break
      default:
        return 'Your DNA is not from this planet'
    }
  }
  return result
};

// Tests
const cases = [
  {
    label: 'ATTGC',
    input: DNA_strand('ATTGC'),
    shouldBe: 'TAACG'
  },
  {
    label: 'GTTAAC',
    input: DNA_strand('GTTAAC'),
    shouldBe: 'CAATTG'
  },
  {
    label: 'AAAA',
    input: DNA_strand('AAAA'),
    shouldBe: 'TTTT'
  },
  {
    label: 'Invalid DNA',
    input: DNA_strand('CTHCC'),
    shouldBe: 'Your DNA is not from this planet'
  }
]

cases.map(test => console.log((test.input === test.shouldBe ? '✅' : '❗') + '  ' + test.label + ' => ' + 'Should be: ' + test.shouldBe + ' received: ' + test.input))