power-assert, mechanism and philosophy

1. power-assert mechanism and philosophy Takuto Wada (a.k.a id:t-wada or @t_wada) Nov 15, 2014 @ Nodefest Tokyo 2014

2. Takuto Wada id: t-wada @t_wada github: twada

3. agenda •what is power-assert? •mechanism •design philosophy

4. state of JavaScript testing testing framework remote test runner environment assertion library mocking library Plenty of alternatives...

5. 33 Methods!? too much to learn...

6. Something is wrong with arms race among assertion libraries... What if the `assert` is informative enough?

7. power-assert https://github.com/twada/power-assert

8. 1. npm install --save-dev power-assert intelli-espower-loader 2. add "directories" to package.json "directories": { "test": "test" }, 3. change var assert = require('assert'); to var assert = require('power-assert'); 4. mocha --require intelli-espower-loader Just 4 steps

9. assert(typeof item.id === 'strong') | | | | | | | false | | "foo" | Item{id:"foo",name:"bar"} "string" --- [string] 'strong' +++ [string] typeof item.id @@ -1,6 +1,6 @@ str -o +i ng You get this work unobtrusively, fail noisily

10. assert(actual) assert.deepEqual(actual,expected) assert.notDeepEqual(actual,expected) You don t need to memorize assertion APIs any more. Just write simple assert

11. arms race among assertion APIs enrich test vocabulary...resulted in overkill power-assert is a Renaissance of code No more assertion war

12. So, why don t you run with tests?

14. var assert = require('power-assert'); function Item(id, name) { this.id = id; this.name = name; } describe('Item', function () { it('has string id', function () { var item = new Item(1000, 'bar'); assert(assert._expr(assert._capt(assert._capt(typeof assert._capt(assert._capt(item, 'arguments/0/left/argument/object').id, 'arguments/0/left/argument'), 'arguments/0/left') === 'string', 'arguments/0'), { content: 'assert(typeof item.id === 'string')', filepath: 'test/item_test.js', line: 11 })); }); }); var assert = require('power-assert'); function Item (id, name) { this.id = id; this.name = name; } describe('Item', function () { it('has string id', function () { var item = new Item(1000, 'bar'); assert(typeof item.id === 'string'); }); }); But How? test code transpiled to

15. https://speakerdeck.com/michaelﬁcarra/spidermonkey-parser-api-a-standard-for-structured-js-representations new C(1 + a)

16. https://speakerdeck.com/constellation/escodegen-and-esmangle-using-mozilla-javascript-ast-as-an-ir Demo

17. https://speakerdeck.com/constellation/escodegen-and-esmangle-using-mozilla-javascript-ast-as-an-ir Demo

18. 3 essential AST tools •esprima •escodegen •estraverse

19. espoweresprima code AST escodegen AST AST AST code code code espower-source grunt-espower / gulp-espower / espowerify / espower-loader / espower-coﬀee / espower-cli

21. The UNIX Philosophy https://github.com/substack/nodefest-2012

22. Make each program do one thing well https://github.com/substack/nodefest-2012

23. Rule of Composition: Design programs to be connected with other programs. Rule of Modularity: Write simple parts connected by clean interfaces.

24. substack pattern module.exports = function(arg) { // do one thing well };

25. First version (4) •power-assert •empower •espower •grunt-espower Currently (15) • power-assert • empower • power-assert-formatter • espower • espower-source • type-name • stringiﬁer • espurify • escallmatch • grunt-espower • gulp-espower • espowerify • espower-loader • espower-coﬀee • espower-cli modularize

26. Your sensibilities about simplicity being equal to ease of use are wrong. Easy is not simple Simple: objective Easy: relative

27. Easy •power-assert •grunt-espower •gulp-espower •espowerify •espower-loader •espower-cli •espower-coﬀee Simple •espower •espower-source •empower separate `simple` from `easy`

28. wrap-up •No more assertion war •Use JS to modify JS •Separate simple from easy •Make things small and composable

29. power-assert https://github.com/twada/power-assert Thank you!

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