From Library to Tool - power-assert as a General Purpose Assertion Enhancement Tool

@ nodefest 2016

Transcript

1. From Library to Tool power-assert as a General Purpose Assertion Enhancement Tool Takuto Wada Nov 13, 2016 @nodefest 2016
2. Takuto Wada
   Twitter: @t_wada
   github: @twada
3. Do you write tests?
4. l+BWB4DSJQU
   'BUJHVFz
   
5. Testing framework should… Evolve slowly. This gives all the people confidence that their investment won't go to waste. ,FOU
   #FDL
   TBJE IUUQTIPQPSFJMMZDPNQSPEVDUEP
6. There is a clash between constraints. Easy to write vs. Easy to Learn to write ,FOU
   #FDL
   BMTP
   TBJE IUUQTIPQPSFJMMZDPNQSPEVDUEP
7. So I (re)invented power-assert Evolve Slowly + Easy to Learn to Write = power-assert IUUQTHJUIVCDPNQPXFSBTTFSUKTQPXFSBTTFSU
8. const assert = require('power-assert'); describe('Pokemon', () => { it('name', () => { const pokemon = new Pokemon('Pidgey'); assert(pokemon.name === 'Poppo'); }); }); power-assert E FN P
9. assert(pokemon.name === 'Poppo') | | | | | false | "Pidgey" Pokemon{name:"Pidgey"} --- [string] 'Poppo' +++ [string] pokemon.name @@ -1,5 +1,6 @@ P -oppo +idgey power-assert output
10. Stop memorizing tons of assertion APIs. Just create expressions that return a truthy value or not. And power-assert will show it to your right on the screen as part of your failure message without you having to type in a message at all. No API is the best API IUUQTHJUIVCDPNQPXFSBTTFSUKTQPXFSBTTFSU
11. http://codelunch.fm/16/
12. BDIJFWFNFOUT
    JO
     https://npm-stat.com/charts.html?package=power-assert&from=2013-08-21&to=2016-11-13
13. const assert = require('power-assert'); describe('Pokemon', () => { it('name', () => { const pokemon = new Pokemon('Pidgey'); assert(pokemon.name === 'Poppo'); }); }); The last piece
14. const assert = require('assert'); describe('Pokemon', () => { it('name', () => { const pokemon = new Pokemon('Pidgey'); assert(pokemon.name === 'Poppo'); }); }); The last piece E FN P
15. const assert = require('assert'); describe('Pokemon', () => { it('name', () => { const pokemon = new Pokemon('Pidgey'); assert(pokemon.name === 'Poppo'); }); }); We eliminated the last dependency. Now your code does not depend on power-assert
16. 1→0
17. From Library To Tool Your code does not depend on tools explicitly. Means that you can enhance your code outside from your code. Just like code coverage tools.
18. What does this mean for you?
19. 1. Now you can empower any existing assertions without modifying code.
20. 2. Now your code live longer than power-assert. Long live assertions!
21. One More Thing…
22. assertion is not only a technique of testing, but of writing reliable code. …even if you cannot write tests for existing code. →assertive programming
23. 'use strict'; const assert = require('assert'); function add (a, b) { assert(!isNaN(a)); assert.equal(typeof b, 'number'); assert.ok(!isNaN(b)); return a + b; } assert in production code
24. { "env": { "development": { "presets": [ "babel-preset-power-assert" ] }, "production": { "plugins": [ "babel-plugin-unassert" ] } } } .babelrc
25. # calc.js:5 assert(!(isNaN(a) || isNaN(b))) | | | | | | | | | | true NaN | false 3 true false FOBCMF
    QPXFSBTTFSU
    JO
    EFWFMPQNFOU
26. 'use strict'; const assert = require('assert'); function add (a, b) { assert(!isNaN(a)); assert.equal(typeof b, 'number'); assert.ok(!isNaN(b)); return a + b; } unassert in production https://github.com/unassert-js/unassert
27. power-assert unassert require('assert') code in production code under development Thank you!