Theorem application test for Experienced Backend Engineer

flatten-array.js

/*
 * Copyright (c) 2019 <CompanyName>
 * All rights reserved.
 */

'use strict';

function flattenArray(sourceArray) {
    var resultArray = [];
    
    for (var item of sourceArray) {
        if (Array.isArray(item)) {
            resultArray = resultArray.concat(flattenArray(item));
        } else {
            resultArray.push(item);
        }
    }
    
    return resultArray;
}

module.exports = flattenArray;

package.json

{
  "name": "flatten-array",
  "version": "1.0.0",
  "description": "",
  "main": "flatten-array.js",
  "scripts": {
    "test": "mocha"
  },
  "author": "Rosberg Linhares",
  "license": "MIT",
  "devDependencies": {
    "mocha": "^6.1.4"
  }
}

test\test.js

/*
 * Copyright (c) 2019 <CompanyName>
 * All rights reserved.
 */

'use strict';

const assert = require('assert');
const flattenArray = require('../flatten-array.js');

describe('#flattenArray()', function() {
    it('Empty array', function() {
        var resultArray = flattenArray([]);
        assert.deepEqual(resultArray, []);
    });
    
    it('Nested empty arrays', function() {
        var resultArray = flattenArray([ [ ], [ [ ], [ ], [ [ ] ] ] ]);
        assert.deepEqual(resultArray, []);
    });
    
    it('Nested empty arrays with single item', function() {
        var resultArray = flattenArray([ [ ], [ [ ], [ ], [ 5, [ ] ] ] ]);
        assert.deepEqual(resultArray, [ 5 ]);
    });
    
    it('Single items', function() {
        var resultArray = flattenArray([ 5, 7, 1, 3 ]);
        assert.deepEqual(resultArray, [ 5, 7, 1, 3 ]);
    });
    
    it('Single items as array', function() {
        var resultArray = flattenArray([ [ 5 ], [ 7 ], [ 1 ], [ 3 ] ]);
        assert.deepEqual(resultArray, [ 5, 7, 1, 3 ]);
    });
    
    it('Deep level single item', function() {
        var resultArray = flattenArray([ [ [ [ [ 8 ] ] ] ] ]);
        assert.deepEqual(resultArray, [ 8 ]);
    });
    
    it('Deep level mixed', function() {
        var resultArray = flattenArray([ [ [ [ 7 ], [ 4, 5, 6 ], [ ], ], 8, 9 ], 1, [ 2, 3, [ 4 ] ] ]);
        assert.deepEqual(resultArray, [ 7, 4, 5, 6, 8, 9, 1, 2, 3, 4 ]);
    });
    
    it('Theorem test', function() {
        var resultArray = flattenArray([ [ 1, 2, [ 3 ] ], 4 ]);
        assert.deepEqual(resultArray, [ 1, 2, 3, 4 ]);
    });
});