The document discusses the principles of unit testing, emphasizing the importance of test-driven development and the need for tests to maintain high code quality. It covers various testing levels, strategies for improving testability, and provides heuristics for determining test scope. Additionally, it offers practical advice on organizing code and managing dependencies for effective testing.

1. …and why is it (often) not a single class
What’s the “unit” in unit testing
Dennis Doomen

2. About Me
Hands-on architect in the .NET space with 25 years of experience on
an everlasting quest for knowledge to build the right software the right
way at the right time

4. Why is this important?

5. Because we like…
…code that can be changed by any
developer in the team without fear and
with confidence

6. Test Driven
Development in
reality
Design class
responsibilities
Write first test
Generate stubs
Fail for the right
reason
Implement
real deal
Ensure test
succeeds
Identify
alternative
scenarios
Repeat twice
Refactor

7. Pros and cons of
different levels of
testing
Exploratory
Testing
Browser
Testing
HTTP/API Tests
Component/Integration Tests
“Unit” Tests
Scope,
Execution
Time
and
flakiness
Simplicity
&
Ease
of
debugging

8. Some examples

13. Smells & heuristics to find the right scope

14. Designed for
reusability? Then
tested separately

15. Is it an
implementation
detail? Then don’t
test it directly

16. Is the test really
testing the real
surface area?

17. Does refactoring
require rewriting the
tests?

18. Things in
adjacent folders
usually mean
they are separate

19. Returning mocks
from mocks is often
a sign of a scope
issue

20. Tips to improve testability

21. Replace ugly
dependencies with
DIP

22. It’s fine to include
the database in tests

23. It’s fine to test
smaller when it adds
value

24. Don't bother
arguing about “unit”
vs “integration”

25. Organize code by
functional
boundaries

26. Apply DRY within
those boundaries

27. Mock the
dependencies
outside of the
scope

28. A less trivial example

29. Command Handlers
Commands
Domain Model
Event Store
Events
App
Read Data
RavenDB
Projectors
Events
HTTP API
Projections
Events

30. Test Fixture
In-Memory
Event Store
Read
Data
RavenDB
Projectors
Events
HTTP API
Projections
Unit Test
HTTP request
Test Data
Sources: https://tinyurl.com/4sukm55n

31. Ask a great questions
…and win a Jetbrains 1-year license
…ask at fluentassertions.slack.com
…ping me at @ddoomen
…email me at dennis.doomen@avivasolutions.nl