docs: expanding on testing
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You're an engineer. You know how to write code, and writing tests isn't all that
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different. But do you know why we write tests? Do you know when to write one, or
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what kind of test to write? How do you know if a test is a _"good"_ test? This
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document's goal is to give you the tools you need to make those determiniations.
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document's goal is to give you the tools you need to make those determinations.
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Okay. So why do we write tests? To increase our... :drum::
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@ -21,14 +21,16 @@ Okay. So why do we write tests? To increase our... :drum::
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## Kinds of Tests
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Test's buy us confidence, but not all tests are created equal. Each kind of test
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has a different cost to write and maintain. More costly tests
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has a different cost to write and maintain. An expensive test is worth it if it
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gives us confidance that a payment is processed, but it may not be the best
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choice for asserting an element's border color.
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| Test Type | Example | Speed | Cost |
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| ----------- | ------------------------------------------------------------------------------------------ | ---------------- | ------------------------------------------------------------------------ |
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| Static | `addNumbers(1, '2')` was called with a `string`, `int` was expected. | :rocket: Instant | :money_with_wings: |
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| Unit | `addNumbers(1, 2)` returns expected result `3` | :airplane: Fast | :money_with_wings::money_with_wings: |
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| Integration | When I Click "Sign In", the page navigates to the dashboard (with mocked network requests) | :running: Okay | :money_with_wings::money_with_wings::money_with_wings: |
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| End-to-end | When I click "Sign In", the page navigates to the dashboard (with no mocks) | :turtle: Slow | :money_with_wings::money_with_wings::money_with_wings::money_with_wings: |
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| Test Type | Example | Speed | Cost |
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| ----------- | ------------------------------------------------------------------------ | ---------------- | ------------------------------------------------------------------------ |
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| Static | `addNumbers(1, '2')` was called with a `string`, `int` was expected. | :rocket: Instant | :money_with_wings: |
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| Unit | `addNumbers(1, 2)` returns expected result `3` | :airplane: Fast | :money_with_wings::money_with_wings: |
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| Integration | Clicking "Sign In", navigates to the dashboard (mocked network requests) | :running: Okay | :money_with_wings::money_with_wings::money_with_wings: |
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| End-to-end | Clicking "Sign In", navigates to the dashboard (no mocks) | :turtle: Slow | :money_with_wings::money_with_wings::money_with_wings::money_with_wings: |
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### Static Code Analysis
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@ -39,9 +41,9 @@ with the expected paramater types.
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Example Tooling:
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- [ESLint][eslint-rules]
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- [TypeScript][typescript-docs] or Flow
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- [TypeScript][typescript-docs] or [Flow][flow-org]
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Static code analysis can't test business logic.
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Where it falls short: Can't test business logic.
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### Unit Tests
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@ -60,9 +62,13 @@ You're testing implementation details if:
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- IE. Using a private function
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- A refactor can break your tests
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Where it falls short: That you're calling a dependency appropriately.
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### Integration Tests
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...
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Integration tests take things one step further. You
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Where it falls short: That you're passing the right data to your backend.
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### End-to-End Tests
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@ -75,19 +81,36 @@ is testing user authentication. If a user can't sign in to your application,
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it's an emergency. Having a high degree of confidance that users can always
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authenticate is very valuable.
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Where it falls short:
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#### When should we test?
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Mission critical features and functionality. Unsure if we should have a test for
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Mission critical features and functionality, or to cover a large breadth of
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functionality until unit tests catch up. Unsure if we should have a test for
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feature `X` or scenario `Y`? Open an issue and let's discuss.
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## Further Reading
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Okay, so hopefully you have more confidance in your understanding of _why_ we
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test, and the trade-offs we weigh when determining what kind of test should be
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written. For the _how_, check out some of the links below, or read some of the
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existing tests in this repository.
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### General
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- [Assert(js) Conf 2018 Talks][assert-js-talks]
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- [Write tests. Not too many. Mostly integration.][kent-talk] - Kent C. Dodds
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- [I see your point, but…][gleb-talk] - Gleb Bahmutov
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- [Statc vs Unit vs Integration vs E2E Testing][kent-blog] - Kent C. Dodds
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- [Static vs Unit vs Integration vs E2E Testing][kent-blog] - Kent C. Dodds
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(Blog)
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### End-to-end Testing w/ Cypress
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- [Getting Started](https://docs.cypress.io/guides/overview/why-cypress.html)
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- Be sure to check out `Getting Started` and `Core Concepts`
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- [Best Practices](https://docs.cypress.io/guides/references/best-practices.html)
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- [Example Recipes](https://docs.cypress.io/examples/examples/recipes.html)
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<!--
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Links
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-->
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@ -95,6 +118,7 @@ feature `X` or scenario `Y`? Open an issue and let's discuss.
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<!-- prettier-ignore-start -->
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[eslint-rules]: https://eslint.org/docs/rules/
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[typescript-docs]: https://www.typescriptlang.org/docs/home.html
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[flow-org]: https://flow.org/
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<!-- Talks -->
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[assert-js-talks]: https://www.youtube.com/playlist?list=PLZ66c9_z3umNSrKSb5cmpxdXZcIPNvKGw
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[kent-talk]: https://www.youtube.com/watch?list=PLV5CVI1eNcJgNqzNwcs4UKrlJdhfDjshf
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