Array copying 2

index.js

function minusLastItem(array) {
  return array.slice(0, array.length-1);
}

function copyFirstHalf(array) {
  return array.slice(0, array.length / 2); 
}

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

// tests

function testFunctionWorks(fn, input, expected) {
  const result = fn(input);
  if (
    result &&
    result.length === expected.length &&
    result.every(function(item) {
      return expected.indexOf(item) > -1;
    })
  ) {
    console.log('SUCCESS: `' + fn.name + '` works!');
    return true;
  } else {
    console.error('FAILURE: `' + fn.name + '` is not working');
    return false;
  }
}

function runTests() {
  const list = [
    'red bull',
    'monster',
    'amp',
    'rockstar',
    'full throttle',
    'kickstart',
  ];
  const result1 = ['red bull', 'monster', 'amp', 'rockstar', 'full throttle'];
  const result2 = ['red bull', 'monster', 'amp'];
  const list2 = ['lions', 'tigers', 'bears'];
  const result3 = ['lions'];
  
  const testResults = [
    testFunctionWorks(minusLastItem, list, result1),
    testFunctionWorks(copyFirstHalf, list, result2),
    testFunctionWorks(copyFirstHalf, list2, result3)
  ];

  const numPassing = testResults.filter(function(result) {
    return result;
  }).length;
  console.log(numPassing + ' out of ' + testResults.length + ' tests passing.');
}

runTests();

https://repl.it/@liseferguson/Array-copying-II-drill