# Contributing: Tests

> Testing is an opinionated topic. Here is a rough overview of our testing
> philosiphy. See something you want to discuss or think should be changed? Open
> a PR and let's discuss.

Why do we write tests?

- Increase confidance

You're testing implementation details if:

- Your test does something that the consumer of your code would never do.
  - IE. Using a private function
- A refactor can break your tests

## Kinds of Tests

| Test Type | Speed                | Cost                                 |
| --------- | -------------------- | ------------------------------------ |
| Static    | :rocket: Instant     | :money_with_wings:                   |
| Unit      | :airplane: Very Fast | :money_with_wings::money_with_wings: |

### Static Code Analysis

Modern tooling gives us this "for free". It can catch invalid regular
expressions, unused variables, and guarantee we're calling methods/functions
with the expected paramater types.

Example Tooling:

- [ESLint][eslint-rules]
- [TypeScript][typescript-docs] or Flow

Static code analysis can't test business logic.

### Unit Tests

...

### Integration Tests

...

### End-to-End Tests

...

## Further Reading

- [Assert(js) Conf 2018 Talks][assert-js-talks]
  - [Write tests. Not too many. Mostly integration.](https://www.youtube.com/watch?list=PLV5CVI1eNcJgNqzNwcs4UKrlJdhfDjshf) -
    Kent C. Dodds
  -

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[eslint-rules]: https://eslint.org/docs/rules/
[typescript-docs]: https://www.typescriptlang.org/docs/home.html
[assert-js-talks]: https://www.youtube.com/playlist?list=PLZ66c9_z3umNSrKSb5cmpxdXZcIPNvKGw
[testing-trophy]: https://twitter.com/kentcdodds/status/960723172591992832?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E960723172591992832&ref_url=https%3A%2F%2Fkentcdodds.com%2Fblog%2Fwrite-tests
[aaron-square]: https://twitter.com/Carofine247/status/966727489274961920
[gleb-pyramid]: https://twitter.com/Carofine247/status/966764532046684160/photo/3
[testing-pyramid]: https://dojo.ministryoftesting.com/dojo/lessons/the-mobile-test-pyramid
[testing-dorito]: https://twitter.com/denvercoder/status/960752578198843392
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