Breaking down return true to win using properties

Abstract

The idea of return true to win exercises is to find a value such as a given function returns true. Values can be of any types but can also be restricted to objects, arrays, functions depending on the problem statement.

This repository applies property based testing, using framework fast-check, to solve such problems.

Statements have been extracted from https://alf.nu/ReturnTrue

Running it locally

npm install
npm run test

Example of output

The following content is an example of what can be the possible output of the npm run test command. The red status of the steps is totally expected. The entry resulting in the value true is given by the framework as the failing example so failure is the answer here.

In the following extract:

  4) Breaking 'return true to win' using Property based Testing
       transitive:
     Error: Property failed after 3011 tests (seed: 1519757029330): [[],false,[]]

The counterexample is [], false, []. Using it as an input for const transitive = (x,y,z) => x && x == y && y == z && x != z should result to true.

$ npm run test

> breaking-return-true-to-win@1.0.0 test C:\src\breaking-return-true-to-win
> mocha "index.js"



  Breaking 'return true to win' using Property based Testing
    1) id
    2) reflexive
    3) infinity
    4) transitive
    5) peano
    6) ouroborobj
    7) evil1
    8) closure


  0 passing (13s)
  8 failing

  1) Breaking 'return true to win' using Property based Testing
       id:
     Error: Property failed after 1 tests (seed: 1519757018521): [{}]
Got error: Property failed by returning false
      at Object.throwIfFailed (node_modules\fast-check\lib\check\runner\utils\utils.js:73:15)
      at Object.assert (node_modules\fast-check\lib\check\runner\Runner.js:179:19)
      at Context.it (index.js:23:12)

  2) Breaking 'return true to win' using Property based Testing
       reflexive:
     Error: Property failed after 8 tests (seed: 1519757018571): [NaN]
Got error: Property failed by returning false
      at Object.throwIfFailed (node_modules\fast-check\lib\check\runner\utils\utils.js:73:15)
      at Object.assert (node_modules\fast-check\lib\check\runner\Runner.js:179:19)
      at Context.it (index.js:29:12)

  3) Breaking 'return true to win' using Property based Testing
       infinity:
     Error: Property failed after 35776 tests (seed: 1519757018574): [0,0]
Got error: Property failed by returning false
      at Object.throwIfFailed (node_modules\fast-check\lib\check\runner\utils\utils.js:73:15)
      at Object.assert (node_modules\fast-check\lib\check\runner\Runner.js:179:19)
      at Context.it (index.js:35:12)

  4) Breaking 'return true to win' using Property based Testing
       transitive:
     Error: Property failed after 3011 tests (seed: 1519757029330): [[],false,[]]
Got error: Property failed by returning false
      at Object.throwIfFailed (node_modules\fast-check\lib\check\runner\utils\utils.js:73:15)
      at Object.assert (node_modules\fast-check\lib\check\runner\Runner.js:179:19)
      at Context.it (index.js:41:12)

  5) Breaking 'return true to win' using Property based Testing
       peano:
     Error: Property failed after 36 tests (seed: 1519757031015): [9007199254740991]
Got error: Property failed by returning false
      at Object.throwIfFailed (node_modules\fast-check\lib\check\runner\utils\utils.js:73:15)
      at Object.assert (node_modules\fast-check\lib\check\runner\Runner.js:179:19)
      at Context.it (index.js:47:12)

  6) Breaking 'return true to win' using Property based Testing
       ouroborobj:
     Error: Property failed after 1319 tests (seed: 1519757031031): [[0]]
Got error: Property failed by returning false
      at Object.throwIfFailed (node_modules\fast-check\lib\check\runner\utils\utils.js:73:15)
      at Object.assert (node_modules\fast-check\lib\check\runner\Runner.js:179:19)
      at Context.it (index.js:53:12)

  7) Breaking 'return true to win' using Property based Testing
       evil1:
     Error: Property failed after 3 tests (seed: 1519757031327): [_ => ""]
Got error: Property failed by returning false
      at Object.throwIfFailed (node_modules\fast-check\lib\check\runner\utils\utils.js:73:15)
      at Object.assert (node_modules\fast-check\lib\check\runner\Runner.js:179:19)
      at Context.it (index.js:59:12)

  8) Breaking 'return true to win' using Property based Testing
       closure:
     Error: Property failed after 136 tests (seed: 1519757031343): [[0]]
Got error: Property failed by returning false
      at Object.throwIfFailed (node_modules\fast-check\lib\check\runner\utils\utils.js:73:15)
      at Object.assert (node_modules\fast-check\lib\check\runner\Runner.js:179:19)
      at Context.it (index.js:65:12)