Talk about unit testing and how it evolved over time, and how to do it well

1. Unit testing done right

2. whoami
• Brian Fenton
• Bigcommerce
• @brianfenton
• Mostly PHP and APIs

3. What is a unit test?
• Small
• Fast
• Tests a single unit <- Here there be dragons

4. Unit?

5. It depends…

6. “A single piece of a class’s
public-facing functionality”

7. History lesson

8. Goals of unit testing over
time
• Find bugs
• Find regressions
• Improve design

9. Philosophies
• Traditional testing
• TDD
• XP
• BDD

10. Behavior vs. Methods

11. https://twitter.com/sarahmei/status/633895726993440768

12. How did we get here?

13. Code coverage

14. "When a measure becomes a target, it
ceases to be a good measure.” -
Goodhart’s Law

15. Different kinds of coverage
• Line
• Function/Method
• Class/Trait

16. Gresham’s Law
/ht @noahsussman

17. Coverage tricks
• if (false) this_function_call_is_covered();
• // @codeCoverageIgnore
• multiple checks on the same line

18. Line coverage can only prove code
wasn’t executed

19. Opcodes

20. Example
for
($i
=
0;
$i
>
10;
$i++)
{
if
($i
%
2
===
0)
{
echo
"Even:
";
}
else
{
echo
"Odd:
";
}
echo
$i,
"n";
}

21. More kinds of coverage
• Opcode
• Branch
• Path

23. Testing your privates
• Don’t!
• Extract functionality to a collaborator or
don’t test it

25. Don’t test your
implementation

26. Flaky tests

27. Flaky tests
• Randomness
• Time/environment
• Network/services

28. Randomness
• Can the randomness come from outside?
• Do you need to know the exact value?
• Can you just verify “randomness”?

29. Namespace trick
namespace
MyNamespace;
function
random()
{
return
mt_rand();
}

30. Namespace trick
namespace
MyNamespace
{
function
random()
{
return
7;
}
}
namespace
MyTests;
…
function
testRandomNumberGenerator()
{
$this-­‐>assertSame(7,
random());
}

31. Environment
• Time
• Shell vars/ini settings/config values
• Filesystem

32. Network/Services

33. Good unit tests
• Single reason to fail
• Clearly named
• testGuestCanRegisterWithValidInformation
• testProcessData

34. Good unit tests
• Easy to read
• Clean
• Arrange, Act, Assert

35. Good unit tests
• Fast
• No side effects

36. Listening to your tests

37. Test smells
• Too many mocks
• Lots of setup required
• Can’t test w/o database/network/etc…
• Can’t inject mocks where needed

38. Test smells
• Mocks returning mocks
• Flaky results
• Unrelated code changes breaking tests
• Testing the implementation

39. Questions?
https://joind.in/14721