Basic Maybe examples using folktale with mocha and expect.js

test.js

const Maybe = require('data.maybe');
const Nothing = Maybe.Nothing;
const Just = Maybe.Just;

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

describe('truth', () => {
    it('will be true', () => {
        expect(true).to.equal(true);
    })
});

// examples from http://robotlolita.me/2013/12/08/a-monad-in-practicality-first-class-failures.html#maybe-things-dont-work
describe('Maybe', () => {
    describe('example uses', ()=> {
        describe('first', () => {
            const first = xs => xs && xs.length > 0 ? Just(xs[0]) : Nothing();
            const concatenate = (ma, mb) => 
              ma.chain(a => mb.chain(b => mb.of(a + b)));

            it('given a collection it must return just the first value', () => {
                const actual = first('abc');
                expect(actual).to.eql(Just('a'));
                expect(actual.isJust).to.be.ok();
            }),
            it('given an empty collection it must return nothing', () => {
                const actual = first([]);
                expect(actual).to.eql(Nothing());
                expect(actual.isNothing).to.be.ok();
            }),
            it('given a null it must return nothing', () => {
                const actual = first(null);
                expect(actual.isNothing).to.be.ok();
            }),
            it('given just two values it must concatenate values', () => {
                var actual = concatenate(Just(1), Just(2));
                expect(actual).to.eql(Just(1 + 2));

                actual = concatenate(Just('Hello '), Just('Mike'));
                expect(actual).to.eql(Just('Hello Mike'));
            }),
            it('given nothing and just a value it must concatenate to nothing', () => {
                var actual = concatenate(Just(42), Nothing());
                expect(actual).to.eql(Nothing());

                actual = concatenate(Nothing(), Just(42));
                expect(actual).to.eql(Nothing());
            }),
            it('given nothing and nothing it must concatenate to nothing', () => {
                const actual = concatenate(Nothing(), Nothing());
                expect(actual.isNothing).to.be.ok();
            }),
            it('given arrays of value it must be able to concatenate them', () => {
                const consonants = 'bcd';
                const vowels     = 'aei';
                const nothing    = []
                
                const firstConsonant = first(consonants);
                const firstVowel     = first(vowels);
                const firstNothing   = first(nothing);

                expect(concatenate(firstVowel, firstNothing)).to.eql(Nothing());
                expect(concatenate(firstVowel, firstConsonant)).to.eql(Just('ab'));
            });
        });
    });
});

Examples are from http://robotlolita.me/2013/12/08/a-monad-in-practicality-first-class-failures.html#maybe-things-dont-work