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
   

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2. Takuto Wada
   Twitter: @t_wada
   github: @twada
   

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3. Do you write tests?
   

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4. l+BWB4DSJQU'BUJHVFz
   

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5. Testing framework should…
   Evolve slowly.
   This gives all the people
   confidence that their
   investment won't go to waste.
   ,FOU#FDLTBJE
   IUUQTIPQPSFJMMZDPNQSPEVDUEP
   

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6. There is a clash
   between constraints.
   Easy to write
   vs.
   Easy to Learn to write
   ,FOU#FDLBMTPTBJE
   IUUQTIPQPSFJMMZDPNQSPEVDUEP
   

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7. So I (re)invented power-assert
   Evolve Slowly + Easy to Learn to Write = power-assert
   IUUQTHJUIVCDPNQPXFSBTTFSUKTQPXFSBTTFSU
   

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8. const assert = require('power-assert');
   describe('Pokemon', () => {
   it('name', () => {
   const pokemon = new Pokemon('Pidgey');
   assert(pokemon.name === 'Poppo');
   });
   });
   power-assert
   E
   FN
   P
   

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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
   

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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
    

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11. http://codelunch.fm/16/
    

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12. BDIJFWFNFOUTJO
    https://npm-stat.com/charts.html?package=power-assert&from=2013-08-21&to=2016-11-13
    

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13. const assert = require('power-assert');
    describe('Pokemon', () => {
    it('name', () => {
    const pokemon = new Pokemon('Pidgey');
    assert(pokemon.name === 'Poppo');
    });
    });
    The last piece
    

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14. const assert = require('assert');
    describe('Pokemon', () => {
    it('name', () => {
    const pokemon = new Pokemon('Pidgey');
    assert(pokemon.name === 'Poppo');
    });
    });
    The last piece
    E
    FN
    P
    

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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
    

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16. 1→0
    

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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.
    

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18. What does this
    mean for you?
    

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19. 1. Now you can
    empower any existing
    assertions without
    modifying code.
    

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20. 2. Now your code
    live longer than
    power-assert.
    Long live assertions!
    

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21. One More Thing…
    

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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
    

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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
    

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24. {
    "env": {
    "development": {
    "presets": [
    "babel-preset-power-assert"
    ]
    },
    "production": {
    "plugins": [
    "babel-plugin-unassert"
    ]
    }
    }
    }
    .babelrc
    

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25. # calc.js:5
    assert(!(isNaN(a) || isNaN(b)))
    | | | | | |
    | | | | true NaN
    | false 3 true
    false
    FOBCMFQPXFSBTTFSUJOEFWFMPQNFOU
    

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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
    

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27. power-assert
    unassert
    require('assert')
    code in production
    code under development
    Thank you!
    

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