1. Dror Helper
Senior consultant
Tuesday, July 23, 2013
What’s wrong with TDD

2. • Software developer & Architect > 10 years
• Senior Consultant
• Agile evangelist
• Blogger – http://blog.drorhelper.com
About.Me

3. What is a unit test?
A method (Code)
that
tests specific functionality,
Has
clear pass/fail criteria
and
runs in isolation

4. This is a unit test!
[TestMethod]
public void CheckPassword_ValidUser_ReturnTrue()
{
bool result = CheckPassword(“user”, “pass”);
Assert.IsTrue(result);
}

5. What about TDD?
Red
Write a failing test
Green
Make the test pass
Refactor
Clean duplicates and tidy up your code

6. In other words:
Write
new
Test
Run
Test
Write
code
Run
Tests
Refactor

7. WHY DOESN’T EVERYBODY DOING IT?
If it’s so simple
7

8. Writing tests takes time which I don’t have
or
Writing tests is a waste of time
and besides
Testing is a tester’s job
Reason #1 – it got “Tests” in it

9. But it takes too much time
120%
135%
115%
125%
0%
20%
40%
60%
80%
100%
120%
140%
IBM: Drivers MS: Windows MS: MSN MS: VS
Time taken to code a feature
WithoutTDD Using TDD

10. Is it a waste of time?
61%
38%
24%
9%
0%
20%
40%
60%
80%
100%
120%
140%
IBM: Drivers MS: Windows MS: MSN MS: VS
Using Test Driven Design
Time To Code Feature Defect density of team

11. Tests costs more time
However
Development takes less Time:
• Less defects
• Rarely need to invoke the debugger
• Every line has a test
• Overcome analysis-paralysis
So do testing waste time?

12. Hope Driven Development
Can you guarantee there won’t be regression?
How do you know that no stupid bugs were
created?
Not testing is a decision

13. Writing tests before coding is counterintuitive
How can you know what you’re going to write?
Planning for failure feels wrong
Reason #2 – Tests before code is wierd

14. • Seems more logical
• Don’t confuse me with new methodologies
• Just as good as tests before
And Finally - no one would ever know
It’s hard to verify were written using TDD
I’ll write the tests after

15. When you write the tests after the code
You Miss the point of TDD:
Emergent Design
Only write the code you
need
TDD is not about the tests

16. Development Driven Tests

17. Video streaming
UI
Closed architectures
Legacy code
If I can’t write tests – how can I use TDD?
Reason # 3 – Not everything is testable

18. You can still test business logic
Use mocking solutions
Remember – TDD is iterative
Not everything is testable - but

19. If you need to
change your code
You have to
Change your tests
Reason #4 – TDD locks design

20. Ideally
Only requirement change (or defect)
would cause tests to break
It means
You have to know how to write robust unit tests
Tests are code too

21. Requires time investment
Counter intuitive
New skill to learn
Might not work for all scenarios
TDD is:

22. a safety net against regression
prevents defects during development
Enabler of modular, testable code
Only write the code you need
Takes less time than DDT
If done correctly …
TDD is also:

23. There are many excuses
not to use TDD
At least try it out before deciding against it.

24. Presenter contact details
C: 972.05.7668543
e: drorh@codevalue.net
B: blog.drorhelper.com
w: www.codevalue.net