Testing Legacy CodeExciting approach to unit testing any code,Keeping high quality & agility, and Creating wicked applications

Eli Lopian, Founder Typemock

WHAT YOU WILL

LEARN

• Problems with legacy code • How isolation helps • How to unit test legacy code (demo)

Legacy code is… Code without testsMichael Feathers

Developers write millions of lines of legacy code

every day!

Legacy Code Problems

• Code is tangled• Complex Tests• Death spiral• Catch-22

Isolate it… (The most effective way to test legacy code )

• Fake Dependencies

• Change Code Behavior

• Verify Calls

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

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

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

Cannot call constructor because of dependencies

Need method to return fake value

Nothing to assert

Fake an object to change its behavior.

Need to change behavior of a private method

Need to Fake an object that is created in the code

• Isolate Dependencies

• Control Behavior

• Assert Calls

Fake It Till You Make It!

PowerfulMocking

Visual Coverage SmartRunner

Typemock Isolator

Productivity*

* Complete Edition Only

• Trial License• Online webinars• Cookbook• Team Demonstration

You can get more resources

www.typemock.com

blog.typemock.com

@typemock

eli@typemock.com

Questions?

Image creditsflickr@33909700@N02flickr@jamesukflickr@nikioflickr@duchampflickr@kalyan02flickr@clarkstonscampflicker@95786359@N05