Unit Testing and its more proactive version Test Driven Development have both opponents as well as proponents. And I get why. It's not easy to do, and if you do it wrong, it hurts. I've shot myself in the feet more than once. But if you do it right, you'll never want to go back to a situation where you don't write tests for all your code. That's what let me to create a popular .NET framework like Fluent Assertions. But TDD doesn't mean you really need to write all tests upfront. The reality is much more pragmatic than the books like you to believe. And this isn't just about test code. A big chunk (if not all) of unit testing and TDD is about designing your solution to be testable. In this talk I'll share everything I've learned over 15 years of practicing Test Driven Development. I'll cover topics like - The value of unit testing and TDD - How to be pragmatic with TDD - How architecture and code design affects testability - How to find the right scope of testing - Tips to write tests that are self-explanatory

1. 15 years of insights
from a TDD
practitioner
Dennis Doomen
@ddoomen | Principal Consultant | Microsoft MVP

2. About Me
• Coding Architect
• .NET/C#
• Bit of TS/JS/React/Vue
• 28 years of experience
• Author of Fluent Assertions,
LiquidProjections, ChillBDD, Reflectify
• www.dennisdoomen.com
• BlueSky, Twitter, Mastodon, LinkedIn

3. What is this all about?

4. Test Driven Development can…
• …allow you to test things in isolation
• …help you design your code properly
• …give you and others confidence
• …be used as documentation
• …keep you out of the debugger hell.
@ddoomen | Principal Consultant | Microsoft MVP

5. The pragmatic
approach to TDD
Design
responsibilities
Write first test
Generate stubs
Fail (for the
right reason)
Implement
Ensure test
succeeds
Alternative
scenarios
Repeat twice
Refactor
@ddoomen | Principal Consultant | Microsoft MVP

6. Rules & Heuristics

7. Treat tests as
specifications
@ddoomen | Principal Consultant | Microsoft MVP

8. Coverage is a
means, not an end
@ddoomen | Principal Consultant | Microsoft MVP

9. Start by reviewing
the tests
@ddoomen | Principal Consultant | Microsoft MVP

10. Use grey box
testing
@ddoomen | Principal Consultant | Microsoft MVP

11. Use multiple levels
of testing
@ddoomen | Principal Consultant | Microsoft MVP
Exploratory
Testing
Browser
Testing
HTTP & API
Tests
Component &
Integration Tests
Unit Tests
Execution
Time
and
flakiness
Simplicity
&
Ease
of
debugging

12. @ddoomen | Principal Consultant | Microsoft MVP
Choose the
right scope

13. Sync folder
structures
@ddoomen | Principal Consultant | Microsoft MVP

14. Use concise fact-
based naming
@ddoomen | Principal Consultant | Microsoft MVP

15. Emphasize the
cause and effect
@ddoomen | Principal Consultant | Microsoft MVP

16. Show the
important stuff
@ddoomen | Principal Consultant | Microsoft MVP

17. Hide the
unimportant stuff
@ddoomen | Principal Consultant | Microsoft MVP

18. Example

19. Stay way from
fixture classes
@ddoomen | Principal Consultant | Microsoft MVP

20. Have clear
assertions
@ddoomen | Principal Consultant | Microsoft MVP

21. Don’t test
implementation
details
@ddoomen | Principal Consultant | Microsoft MVP

22. Don’t overuse
mocking
@ddoomen | Principal Consultant | Microsoft MVP
Service Service
Service Service
Service
Centralized
Service
Can use mocking
Can use
mocking
Can use mocking
Can use
mocking
Avoid
mocking
Avoid
mocking
Avoid
mocking

23. It’s okay to use a
real database
@ddoomen | Principal Consultant | Microsoft MVP
Characteristics Test Suite
Application
Legacy Code Base
Linux Test Container
SQL Server

24. Don’t give people
an excuse to not
run the tests
@ddoomen | Principal Consultant | Microsoft MVP

25. Don’t accept
flakiness
@ddoomen | Principal Consultant | Microsoft MVP

26. Introduce
characterization
tests
@ddoomen | Principal Consultant | Microsoft MVP
Characteristics Test Suite
Application
Legacy Code Base
Production Backup

27. Find me at
twitter: ddoomen
mastodon: @ddoomen.mastodon.social
bluesky: @ddoomen.bsky.social
email: dennis.doomen@avivasolutions.nl
slack: fluentassertions.slack.com

28. Bonus Content