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From Library to Tool
power-assert as a
General Purpose Assertion
Enhancement Tool
Takuto Wada
Nov 13, 2016 @nodefest 2016
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Takuto Wada
Twitter: @t_wada
github: @twada
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Do you write tests?
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l+BWB4DSJQU'BUJHVFz
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Testing framework should…
Evolve slowly.
This gives all the people
confidence that their
investment won't go to waste.
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There is a clash
between constraints.
Easy to write
vs.
Easy to Learn to write
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So I (re)invented power-assert
Evolve Slowly + Easy to Learn to Write = power-assert
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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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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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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
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http://codelunch.fm/16/
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https://npm-stat.com/charts.html?package=power-assert&from=2013-08-21&to=2016-11-13
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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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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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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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1→0
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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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What does this
mean for you?
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1. Now you can
empower any existing
assertions without
modifying code.
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2. Now your code
live longer than
power-assert.
Long live assertions!
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One More Thing…
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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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'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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{
"env": {
"development": {
"presets": [
"babel-preset-power-assert"
]
},
"production": {
"plugins": [
"babel-plugin-unassert"
]
}
}
}
.babelrc
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# calc.js:5
assert(!(isNaN(a) || isNaN(b)))
| | | | | |
| | | | true NaN
| false 3 true
false
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'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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power-assert
unassert
require('assert')
code in production
code under development
Thank you!