Writing Minitest clone in 30 minutes

https://2023.rubyconf.tw/

Transcript

1. Writing Minitest clone in 30 minutes RubyConfTw 2023 OKURA Masafumi, 2023-12-16
2. Minitest
3. Have you used it?
4. Features
5. Features of Minitest • Just Ruby • No DSL • Fast • Supports spec style testing • describe, it, etc. • Clean and readable
6. Features of Minitest • Just Ruby • No DSL • Fast • Supports spec style testing • describe, it, etc. • Clean and readable
7. Readable test code
8. What about internal code?
9. Let’s battle!
10. Lines of code
11. Minitest:
12. 2000!
13. RSpec:
14. 7800!
15. … only for rspec-core gem
16. Much smaller codebase
17. Question: Can I write my own Minitest?
18. Let’s do it!
19. Me • Name: OKURA Masafumi (େ૔խ࢙) • From: Tokyo, Japan • Work: Freelance web developer (Rails) • Activities: Kaigi on Rails, Alba, etc. • Hobbies: Coffee, learning languages including Chinese • Development environment: Neovim, iTerm2, zsh
20. About this talk
21. Live coding
22. Goal: Writing something similar to Minitest
23. … in 30 minutes
24. Using my own dev env
25. Let’s go!
26. Wrapping up
27. What Minitest does • `ruby sample_test.rb` evaluates test fi le • Instance methods including `setup` are de fi ned, no class methods are de fi ned • All instance methods whose name start with `test_` are recognized as test methods • Inside test methods there are assertion methods • When assertion methods are executed it stores results, and when the result is failure the execution stops • It produces some outputs like "2 runs, 3 assertions, 0 failures"
28. Problems • There's no explicit step to execute tests • There's no explicit step to create an instance of the test class • Not all methods are test methods • Tests whose name do not start with `test_` are simply helper methods • It needs to collection results
29. Solutions • We can use `at_exit` hook to execute test • Alternatively, we can use `ObjectSpace` module to get all classes with `Test` suf fi x, but this is much more complicated • Inside `at_exit` hook we can create an instance of the test class • We can use `method_added` hook to check the name and if it matches `test_` pre fi x it's marked as a test method. • We can store results in an instance variable
30. Summary
31. Takeaways
32. at_exit
33. at_exit • Executed when Ruby interpreter exits • Not suitable for a large business logic, but convenient for smaller tasks • https://docs.ruby-lang.org/en/master/Kernel.html#method-i-at_exit
34. class_eval
35. some_class.class_eval(&block) • Executes given block as if it’s in the class • The argument can be a String instead of a block, but block form is often preferred • Useful if we want to do a lot of thing for that class • https://docs.ruby-lang.org/en/master/Module.html#method-i- class_eval
36. inherited
37. def self.inherited(subclass) • Can be used when subclass needs some behavior • `subclass` argument is a `Class` object, so we can call `class_eval`, `include` or `extend` on it • Don’t forget to call `super` • https://docs.ruby-lang.org/en/master/Class.html#method-i- inherited
38. method_added
39. def self.method_added(name) • Lesser known, less frequently used • Can be used when we want to categorize methods, treat some methods as special ones, and customize each method • When customize, it’s often used with `method` and `de fi ne_method` method • https://docs.ruby-lang.org/en/master/Module.html#method-i- method_added
40. Designing
41. Designing a framework/library • Be familiar with the features the language gives us • In Ruby, there are varieties of hooks • Think of usages, rather than implementations • Autorun is a optional but useful feature, so we want it • Consider where to put what data • In more complex case, more data would be stored in its own place
42. And fi nally
43. Learning is fun
44. Coding is fun!
45. Happy coding!