JS Bin// source https://jsbin.com/xudijag

Temperature conversion.html

function celsToFahr(celsTemp) {
  //[°C] ×  9⁄5 + 32
  return (celsTemp * 9 / 5) + 32
}

function fahrToCels(fahrTemp) {
  //([°F] − 32) ×  5⁄9
  return (fahrTemp - 32) * (5 / 9)
}


/* From here down, you are not expected to 
   understand.... for now :)  
   
   
   Nothing to see here!
   
*/



// tests

function testConversion(fn, input, expected) {
  if (fn(input) === expected) {
    console.log('SUCCESS: `' + fn.name + '` is working');
    return true;
  }
  else {
    console.log('FAILURE: `' + fn.name + '` is not working');
    return false;
  }
}

function testConverters() {
  var cel2FahrInput = 100;
  var cel2FahrExpect = 212;
  var fahr2CelInput = 32;
  var fahr2CelExpect = 0;
  
  if (testConversion(celsToFahr, cel2FahrInput, cel2FahrExpect) &&
     testConversion(fahrToCels, fahr2CelInput, fahr2CelExpect)) {
    console.log('SUCCESS: All tests passing');
  }
  else {
    console.log('FAILURE: Some tests are failing');
  }
}

testConverters();