Flatten Numerical Array & unit testing

gistfile1.txt

// flatten the array of integers

const flatten = array =>
    JSON.stringify(array)         // JSON encode the array to make string
    .match(/\d+/g)                // extract numbers using regex
    .map(x => parseInt(x));       // convert string to numbers
    
    
// unit testing with Mocha
var assert = require('assert');

describe('flatten', function() {
  it('should flat array of integers', function() {
    const input = [1, [2, 34], 5, 6, [7, 8, 9], 10];
    const expectedOutput = [1, 2, 34, 5, 6, 7, 8, 9, 10];
    const output = flatten(input);
    
    assert.equal(JSON.stringify(output), JSON.stringify(expectedOutput));
  });
});