Tests from the crypt

Terrifying true tales of Node.js test-driven-development

Anna Gerber

@AnnaGerber

👌 Tests should be

• 😌 Fast
• 🕵️‍♀️ Clear
• 👍 Reliable
• 🛠 Maintainable

😰 Tests too slow? Benchmark!

• Log start and end times
• Run mocha with the --slow flag
• Use ts:

           mocha test/testThings.js | ts '[%Y-%m-%d %H:%M:%.S]'

😌 Parallelize

😌 Don’t test third party / framework code

😌 Run tests selectively:

Filter on tags / keywords

mocha --grep billing

😨 Unbalanced

Too top-heavy (more E2E or integration tests than unit tests)

😱 Buried (in setup / teardown)

😌 Fixtures

• Provide a baseline for data but also makes setup less transparent
• Alternatively, speed up setup by:
  • Using in-memory or mocked db
  • Batching db writes

😱 Enigmatic tests

🕵️‍♀️ Clear descriptions

- pinpoint where things went wrong

• Unique to each test
• Include the component, scenario, and expected outcome
• Easy to find - don't use templates or functions to generate descriptions!!!

🕵️‍♀️ Targeted assertions
- pinpoint what went wrong

• Using chai assert - provide human readable messages 
• Be specific - don't use deep equal assertions everywhere

🕵️‍♀️ Decipherable data

🕵️‍♀️ Avoid abstraction

• Be explicit
• Use helpers judiciously to hide boilerplate / setup / teardown
• Avoid hiding test assertions in helpers

😨 Flickering tests

• Race conditions in tests
• Mocha scope issues

👍 Kill unreliable tests 🔪

👍 Don't just test the happy path

👍 Test against contracts

🛠 Refactor your tests!

• red / green / refactor applies to tests as well as code
• periodically review / refactor all tests (not just new ones)
• reliable tests are as valuable as reliable application code

🛠 Write standalone tests

🛠 Re-use appropriately

🛠 Mind your mocks

🧘‍♂️ Be mindful

• up-front cost of writing the test
• cost of running this test over time
• cost of maintaining this test over time
• balance against the benefit of the test

Tests from the crypt

Anna Gerber

PCCW Global - we are hiring 😊

@AnnaGerber