Basic example of folktale core.check with mocha, expect.js, and jsverify

test.js

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

const check = require('core.check');

describe('core.check', () => {
  describe('given the right type it must pass', () => {
    jsc.property('given an int when an int is expected it must pass', jsc.int16,
      n => check.assert(check.Number(n)) === n
    ),
    jsc.property('given a string when an string is expected it must pass', jsc.string,
      s => check.assert(check.String(s)) === s
    ),
    jsc.property('given either a string or int when either a string or int is expected it must pass', jsc.bool, jsc.string, jsc.int16,
      (pred, s, n) => {
        const value = pred ? s : n;
        return check.assert(check.Or([check.String, check.Number])(value)) === value;
      }
    ),
    jsc.property('given a string when one is expected it must pass', jsc.string,
      s => check.String(s).cata({
        Failure: e => "Something went very wrong!",
        Success: r => r === s
      })
    ),
    jsc.property('given a string and int when it is expected a string and int it must pass', jsc.string, jsc.int32,
      (s, n) => {
        const pattern = check.Seq([check.String, check.Number]);
        const value = [s, n];
        return check.assert(pattern(value)) === value;
      }),
    jsc.property('given a string and int with others when it is expected a string and int it must pass', jsc.string, jsc.int32, jsc.bool, jsc.asciichar,
      (s, n, b, c) => {
        const pattern = check.Seq([check.String, check.Number]);
        const value = [s, n, b, c];
        return check.assert(pattern(value)) === value;
      });
  }),
  describe('given the wrong type it must fail', () => {
    it('given an int when a string is expected it must fail', () => {
      expect(() => check.assert(check.String(1))).to.throwError();
    }),
    it('given a string when an int is expected it must fail', () => {
      expect(() => check.assert(check.Number("1"))).to.throwError();
    }),
    it('given neither a string nor an int when it expects either then it must fail', () => {
      expect(() => check.assert(check.Or([check.String, check.Number])({something: "else"})));
    }),
    it('given a bool when it expected a string it must fail', () => {
      expect(check.String(false).cata({
        Failure: e => "Ummm that is a boolean",
        Success: s => "How the hell did we get here?"
      })).to.eql("Ummm that is a boolean");
    }),
    it('given a string and int when it expects only strings it must fail', () => {
      expect(() => check.assert(check.Seq([check.String, check.String])(["pass", 1]))).to.throwError();
    });
  });
});