This document discusses strategies for modernizing legacy code through an iterative process. It recommends starting by breaking dependencies with minimal changes while applying tests. Small changes should then be made and tests cleaned up before refactoring code to a cleaner state. The document outlines approaches like partial mocking, dependency injection, and out-of-context testing to break dependencies in an untestable code. It stresses adding tests incrementally and refactoring both production code and tests as the process continues.

1. Modernising Legacy
Code
Sam Harwood

2. What is Legacy Code?
Old
Fragile
Incomprehensible
Not under test

3. Why Modernise Legacy Code?
New development
Bug fixes
Change requests
To reduce maintenance costs

4. When to Refactor Legacy Code
There's no smoke...
'It's not safe to refactor'
Key element of application
'My boss told me not to'

5. An Iterative Approach
Start small
Identify target areas
Deploy, deploy, deploy!

6. Process Plan
Break dependencies with minimal changes;
apply tests
Make small changes
Clean up tests
Refactor to clean code

7. Untestable Behaviour
DB connectivity
Web services
Global vars
exit();
File work
System calls
echo(), print(), var_dump(), …
Memcache etc.

8. How to Break Dependencies
Partial mockery
Dependency injection
Out-of-context testing

9. Option 1: Partial Mockery
public function __construct() {
$dbh = new DbConnection('localhost', 'db', 'user', 'pass',
3306);
if ($dbh->connection_fail) {exit;}
if ($GLOBALS['debug mode']) {
print 'Constructing!';
}
$this->doOtherThings();
}

10. Partial Mocks cont.
public function __construct() {
$dbh = $this->_getDbConnection();
//...
}
/**
* @return DbConnection
*/
protected function _getDbConnection() {
return new DbConnection('localhost', 'db', 'user', 'pass',
3306);
}

11. Partial Mocks cont.
public function setUp() {
$this->_objectUnderTest = $this->getMock('MyClass',
array('_getDbConnection', '_doExit', '_sendHttpQuery'),
array(), '', '', true);
$this->_mockDbConnection = $this->getMock('DbConnection');
$this->_objectUnderTest->expects($this->any())
->method('_getDbConnection')
->will($this->returnValue($this->
_mockDbConnection));
}

12. Option 2: Dependency Injection
public function __construct() {
$dbh = $this->_yadifContainer->getComponent('DbConnection');
//...
}

13. Option 3: Out-of-Context Testing
Fake objects
set_include_path('');
runkit.internal_override &
runkit_function_redefine()

14. Next Steps
Provide satisfactory test coverage, and
refactor...
Add tests for constructor
Comment code to help plan tests
Cover other code addressed in this iteration

15. Add Comments...
public function massiveMethod($param = 'hello world') {
// Check if DB knows how awesome we are
$dbConnection = $this->_getDbConnection();
$resultSet = $dbConnection->executeSql(
'SELECT group_of_developers FROM london WHERE everyone_is
LIKE "%we're the best php%" GROUP BY miles');
$dbRes = count($resultSet) > 0;
// Calculate something else
$aString = $param;
$aString .= 'more string';
$aString .= 'more string';
$aString .= 'more string';
$aString .= 'more string';

16. ...Remove Comments
public function massiveMethod($param = 'hello world') {
$dbRes = $this->_checkIfDbKnowsHowAwesomeWeAre();
$aString = $this->_generateSomeString($param);

17. Things to Bear in Mind When
Breaking Up Large Functions
Method name reflects comment
Test section before moving it
Parameter count

18. Looking Inside Large Methods
Sensing variables
if () {
foreach () {
if () {
$this->_privateAttrib = 'something';
$this->sensingVariable = true;
}
}
}
Indecent exposure
Partially mock most of class

19. Cleaning Up Production Code
Minimise public API
Remove unnecessary comments
Roll out dependency injection
Be sure to remove methods for partial
mocking

20. Refactoring Tests
Inject mock objects via DI
Stop testing partial mock
Remove 'out-of-context' setup
Remove single-line constructor tests,
sensing variable tests etc.

21. Summary
Break dependencies
Apply tests
Refactor production code
Refactor tests

22. samthephpdev@gmail.com
@AgileTillIDie