Chai formatArray when Array.prototype has been modified.

chai-noisy-arrays.js

const expect = require('chai').expect;

Array.prototype.doubleAll = function() {
  return this.map(a => a * 2);
};

describe("Arrays", function() {
  describe("doubleAll method", function() {
    it("should exist on all arrays", function() {
      expect([].doubleAll).to.be.instanceof(Function);
      expect(new Array().doubleAll).to.be.instanceof(Function);
    });

    it("should double all values in the array", function() {
      // intentionally broken
      expect([ 1, 2, 3, 4 ].doubleAll()).to.eql([ 2, 4, 6, 9 ]);
    });
  });
});

/* Test Output

$ mocha test.js -R tap

1..2
ok 1 Arrays doubleAll method should exist on all arrays
not ok 2 Arrays doubleAll method should double all values in the array
  AssertionError: expected [ 2, 4, 6, 8, doubleAll: [Function] ] to deeply equal [ 2, 4, 6, 9, doubleAll: [Function] ]
      at Context.<anonymous> (/Users/michaellange/work/chai-inspect-test/test.js:16:42)
      at callFn (/usr/local/lib/node_modules/mocha/lib/runnable.js:266:21)
      at Test.Runnable.run (/usr/local/lib/node_modules/mocha/lib/runnable.js:259:7)
      at Runner.runTest (/usr/local/lib/node_modules/mocha/lib/runner.js:387:10)
      at /usr/local/lib/node_modules/mocha/lib/runner.js:470:12
      at next (/usr/local/lib/node_modules/mocha/lib/runner.js:312:14)
      at /usr/local/lib/node_modules/mocha/lib/runner.js:322:7
      at next (/usr/local/lib/node_modules/mocha/lib/runner.js:257:23)
      at Immediate._onImmediate (/usr/local/lib/node_modules/mocha/lib/runner.js:289:5)
      at processImmediate [as _immediateCallback] (timers.js:383:17)
# tests 2
# pass 1
# fail 1

*/