Example of using property based testing with jsverify

example.jsverify.spec.coffee

# Assume this is a spec file to run in Mocha. This is an artificial example
# that tries to show the general idea of incorporating property based testing.


jsc      = require 'jsverify'
mySorter = require '../src/mySorter'


describe 'My sorting algorithm', ->
  ######################################################
  ## First, unit tests to drive implementation design
  ######################################################
  it 'should put apa before bepa', ->
    # given
    input    = ['bepa', 'apa']
    expected = ['apa', 'bepa']
    output   = mySorter(input)

    # then
    expect(output).to.eql expected


  it 'should put bepa before cepa', ->
    # given
    input    = ['ccccc', 'bepa']
    expected = ['bepa', 'ccccc']
    output   = mySorter(input)

    # then
    expect(output).to.eql expected

    
  ######################################################
  ## Then, properties that should hold in general
  ######################################################
  jsc.property 'should sort by length', 'array string', (input) ->
    sorted = mySorter(input)

    for i in [1..sorted.length]
      if sorted[i-1].length > sorted[i].length
        return false
      
    return true