The document discusses strategies for unit testing legacy code, emphasizing the importance of isolating dependencies and using fakes to enhance testability. It highlights the common challenges developers face with tangled and complex legacy code and demonstrates how the 'isolate' approach enables effective testing. Resources for further learning and tools offered by Typemock are also mentioned.

1. Testing Legacy Code
Exciting approach to unit testing any code,
Keeping high quality & agility, and
Creating wicked applications
Eli Lopian,
Founder Typemock

2. WHAT
YOU
WILL
LEARN
• Problems with legacy code
• How isolation helps
• How to unit test legacy code (demo)

3. Legacy code is… Code without tests
Michael Feathers

4. Developers write millions of lines
of legacy code
every day!

5. Legacy Code Problems
• Code is tangled
• Complex Tests
• Death spiral
• Catch-22

6. Isolate it… (The most effective way to test legacy code )
• Fake Dependencies
• Change Code Behavior
• Verify Calls

7. Fake Dependencies
var fakeProcess = Isolate.Fake.Instance<Process>();
fakeProcess.MainModule.Site.Name
var fakeProcessHandle = Isolate.Fake.NextInstance<Process>();
var fakeAllProcessHandle = Isolate.Fake.AllInstances<Process>();
var fakeSimulator = Isolate.Fake.Dependencies<Simulator>();
Create a fake instance of a type:1
Signal that the next instance will be faked:2
Fake ALL the dependencies that are passed through the constructor:3

8. Change Code Behavior
Isolate.WhenCalled(() => DateTime.Now).WillReturn(new DateTime(1977,5,25));
Isolate.WhenCalled(() => fake.MainModule.Site.Name).WillReturn("Typemock rocks");
var counter = new Counter ();
Isolate.WhenCalled(() => counter.Increment()).WillReturn(1);
Isolate.WhenCalled(() => counter.Increment()).WillReturn(2);
Change return value of a static method:1
Change return value of a chain of calls:
Change return value of a method from a real object:
2
3

9. Verify Calls
Isolate.Verify.WasCalledWithAnyArguments(() => backoffice.Save());
Isolate.Verify.WasNotCalled(() => backoffice.Save());
int count = Isolate.Verify.GetTimesCalled(() => backoffice.Save());
Assert.AreEqual(2, count);
The code called Save():
The code never calls Save():
The code calls the method 2 times:
1
2
3

11. Cannot call constructor because of dependencies

12. Need method to return fake value

13. Nothing to assert

14. Fake an object to change its behavior.

15. Need to change behavior of a private method

16. Need to Fake an object that is created in the code

17. • Isolate Dependencies
• Control Behavior
• Assert Calls
Fake It Till You Make It!

18. Powerful
Mocking
Visual
CoverageSmartRunner
Typemock Isolator
Productivity*
* Complete Edition Only

19. • Trial License
• Online webinars
• Cookbook
• Team Demonstration
You can get more resources

20. www.typemock.com
blog.typemock.com
@typemock
eli@typemock.com
Questions?
Image credits
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