This document discusses strategies for testing code that is difficult or impossible to test directly. It begins by defining "untestable code" as code with tight coupling, dependencies on external resources, or other factors that prevent direct testing. The document then explores approaches like refactoring code to loosen dependencies and increase testability, using techniques like dependency injection and mocking external resources. It also discusses more advanced approaches like generative programming, where a framework can automatically generate test doubles and modify code structure to enable automated testing. The overall message is that with creativity, even legacy or complex code can be made testable through approaches that control dependencies and isolate the system under test.

1. Testing untestable code
Stephan Hochdörfer, bitExpert AG

2. Testing untestable code
About me
 Stephan Hochdörfer, bitExpert AG
 Department Manager Research Labs
 S.Hochdoerfer@bitExpert.de
 @shochdoerfer

3. Testing untestable code
No excuse for writing bad code!

4. Testing untestable code
Not to freak out!

5. Testing untestable code
Creativity matters!

6. Testing untestable code
"There is no secret to writing tests,
there are only secrets to write
testable code!"
Miško Hevery

7. Testing untestable code
What is „untestable code“?

8. Testing untestable code
Wrong object construction
“new” is evil!
s

9. Testing untestable code
Tight coupling

10. Testing untestable code
Uncertainty

11. Testing untestable code
"...our test strategy requires us to
have more control [...] of the sut."
Gerard Meszaros, xUnit Test Patterns: Refactoring Test
Code

12. Testing untestable code
In a perfect world...
Unittest
Unittest SUT
SUT

13. Testing untestable code
Legacy code is not perfect...
Dependency
Dependency
Unittest
Unittest SUT
SUT
Dependency
Dependency

14. Testing untestable code
...
Legacy code is not perfect...
Dependency
Dependency
Unittest
Unittest SUT
SUT
Dependency
Dependency
...

15. Testing untestable code
...
Legacy code is not perfect...
Dependency
Dependency
Unittest
Unittest SUT
SUT
Dependency
Dependency
...

16. Testing untestable code
How to get „testable“ code?

17. Testing untestable code
How to get „testable“ code?
Refactoring

18. Testing untestable code
"Before you start refactoring, check
that you have a solid suite of tests."
Martin Fowler, Refactoring

19. Testing untestable code
Hope? - Nope...

20. Testing untestable code
Which path to take?

21. Testing untestable code
Which path to take?
Do not change existing code!

22. Testing untestable code
Examples
Object construction External resources Language issues

23. Testing untestable code
Object construction
public class Car {
private Engine engine;
public Car(String engine) {
this.engine = EngineFactory.getByType(engine);
}
}

24. Testing untestable code
Object construction - Solution
public class MyLoader extends ClassLoader {
protected Class findClass(String name)
throws ClassNotFoundException
{
try {
String path = name.replace('.', '/');
// @TODO: change path and read file,
// @TODO: define package
// @TODO: define class
}
catch(Exception e){
throw new ClassNotFoundException(name);
}
}
}

25. Testing untestable code
Object construction - Solution II
<?php
class MyStreamWrapper {
private $_handler;
function stream_open($path, $mode, $options,
&$opened_path) {
stream_wrapper_restore('file');
// @TODO: modify $path before fopen
$this->_handler = fopen($path, $mode);
stream_wrapper_unregister('file');
stream_wrapper_register('file', 'MyStreamWrapper');
return true;
}
}

26. Testing untestable code
External resources

27. Testing untestable code
External resources
Database Webservice
Filesystem Mailserver

28. Testing untestable code
External resources – Mock database

29. Testing untestable code
External resources – Mock database
Provide own db driver

30. Testing untestable code
External resources – Mock database
junit + dbunit

31. Testing untestable code
External resources – Mock database
Proxy for your SQL Server

32. Testing untestable code
External resources – Mock webservice

33. Testing untestable code
External resources – Mock webservice
Provide own implementation

34. Testing untestable code
External resources – Mock webservice
Do not forget!
Url redirection via /etc/hosts

35. Testing untestable code
External resources – Mock filesystem

36. Testing untestable code
External resources – Mock filesystem
Commons-VFS
vfsStream

37. Testing untestable code
External resources – Mock filesystem
<?php
// set up test environmemt
vfsStream::setup('exampleDir');
// create directory in test enviroment
mkdir(vfsStream::url('exampleDir').'/sample/');
// check if directory was created
echo vfsStreamWrapper::getRoot()->hasChild('sample');

38. Testing untestable code
External resources – Mock Mailserver

39. Testing untestable code
External resources – Mock Mailserver
Use fake mail server

40. Testing untestable code
Dealing with language issues

41. Testing untestable code
Dealing with language issues
Testing your privates?

42. Testing untestable code
Dealing with language issues
final Method methods[] =
o.getClass().getDeclaredMethods();
for (int i = 0; i < methods.length; ++i) {
if (methodName.equals(methods[i].getName())) {
try {
methods[i].setAccessible(true);
return methods[i].invoke(o, params);
}
catch (IllegalAccessException ex) {
}
catch (InvocationTargetException ite) {
}
}
return null;
}

43. Testing untestable code
Dealing with language issues
Overwrite internal functions?

44. Testing untestable code
What else?

45. Testing untestable code
What else?
Generative Programming

46. Testing untestable code
Generative Programming
Configuration
Configuration
1 ... n
Implementation
Implementation Generator
Generator Product
components
components Product
Generator
Generator
application
application

47. Testing untestable code
Generative Programming
Configuration
Configuration
Application
Application
Implementation
Implementation Generator
Generator
components
components
Testcases
Testcases
Generator
Generator
application
application

48. Testing untestable code
Generative Programming
A frame is a data structure
for representing knowledge.

49. Testing untestable code
A Frame instance
public class Car {
private Engine engine;
public Car(String engine) {
this.engine = <!{Factory}!>.getByType(engine);
}
}

50. Testing untestable code
The Frame controller
public class MyFrameController extends
SimpleFrameController {
public void execute(Frame frame, FeatureConfig
config) {
if(config.hasFeature("unittest")) {
frame.setSlot("Factory", "FactoryMock");
}
else {
frame.setSlot("Factory", "EngineFactory");
}
}
}

51. Testing untestable code
Generated result - Testcase
public class Car {
private Engine engine;
public Car(String engine) {
this.engine = FactoryMock.getByType(engine);
}
}

52. Testing untestable code
Generated result - Application
public class Car {
private Engine engine;
public Car(String engine) {
this.engine = EngineFactory.getByType(engine);
}
}

53. Testing untestable code
What is possible?

54. Testing untestable code
What is possible?
Show / hide parts of the code

55. Testing untestable code
What is possible?
Change content of global vars!

56. Testing untestable code
What is possible?
Define pre- or postfixes!

57. Testing untestable code
Is it worth it?

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