A code kata in C# to help practice techniques for safely removing dependencies form legacy code and creating unit tests. Questions? Suggestions? Contact @dubmun.

1. Legacy Code Kata
v3.0
William Munn, CGFWB

2. You Need This Stuff
• Seed Legacy Code
• https://github.com/KatasForLegacyCode/kCSharp/
archive/Step0.zip
• An IDE
• Visual Studio 2012+
• An nUnit test runner (I recommend nCrunch)
• OR Jetbrains Rider

3. Legacy Code

4. Read
This
Book

5. Dependency

7. Code Kata
• A code kata is an exercise in
programming which helps a us hone
our skills through practice and
repetition.
• The word kata is taken from
Japanese arts most traditionally
Martial Arts
• Why a code kata? Because we learn
by doing.
We Begin With Practice

8. Dependency Kata: Initial Structure
DoItAllTests.cs
Database.cs
DoItAll.cs
UserDetails.cs
ConsoleAdapter.cs
Program.cs
Logger.cs
Existing Files
We Will
Create

9. Test1 Test2 Test3 Test4 Build
Dependency Kata: Kata Barometer

10. Dependency Kata: First Things First
Let’s start by trying to get the existing test running.
• Currently, running the integration test times out. Why?
• DEPENDENCIES!
• Begin by abstracting and breaking the dependency on Console.Readline() DoItAll.cs
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11. Dependency Kata: First Things First
We’ll use an adapter, but we could use the Console.SetIn method and a TextReader.
• Create an interface
public interface IConsoleAdapter
{
string GetInput();
}
• Create a class that implements the
interface & implement method to
handle our dependency
public class ConsoleAdapter : IConsoleAdapter
{
public string GetInput()
{
return Console.ReadLine();
}
}
ConsoleAdapter.cs
ConsoleAdapter.cs Did you know?
In software engineering, the adapter
pattern is a software design pattern
that allows the interface of an existing
class to be used as another interface.
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12. Dependency Kata: First Things First
• Create new constructor to accept IConsoleAdapter & set private variable
private readonly IConsoleAdapter _consoleAdapter;
public DoItAll(IConsoleAdapter consoleAdapter)
{
_consoleAdapter = consoleAdapter;
}
DoItAll.cs
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13. Dependency Kata: First Things First
• Replace 4 calls to Console.ReadLine() WITH _consoleAdapter.GetInput()
• Replace 2 calls to Console.ReadKey() WITH _consoleAdapter.GetInput()
DoItAll.cs
DoItAll.cs
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14. Dependency Kata: First Things First
We have broken instantiations of DoItAll
• Instantiate and pass in our new handler
var doItAll = new DoItAll(new ConsoleAdapter());Program.cs
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15. Dependency Kata: First Things First
Let’s update our integration test or it will also fail.
• Create a new implementation of IConsoleAdapter
public class DoItAllTests
{
[…]
var doItAll = new DoItAll(new FakeConsoleAdapter());
[…]
}
public class FakeConsoleAdapter : IConsoleAdapter
{
public string GetInput()
{
return string.Empty;
}
}
DoItAllTests.cs
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16. Dependency Kata: First Things First
• When the test is run we now get a meaningful exception. All of the dependencies that caused
the hang are gone.
• the test is now failing because the password is empty. This is a meaningful case but let’s just
update our fake for now.
public string GetInput()
{
return “someTestString”;
}
DoItAllTests.cs
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17. Dependency Kata: First Things First
• Following good testing practice,
let’s add an assert:
[Test, Category("Integration")]
public void DoItAll_Does_ItAll()
{
var doItAll = new DoItAll(new FakeConsoleAdapter());
Assert.That(() => doItAll.Do(), Throws.Nothing);
}
• Our test should still pass.
DoItAllTests.cs
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18. Dependency Kata: Better Coverage
Some of our legacy code has no coverage and produces no quantifiable results
• Copy the existing test and rename it DoItAll_Fails_ToWriteToDB
[Test, Category("Integration")]
public void DoItAll_Does_ItAll()
{
[…]
}
[Test, Category("Integration")]
public void DoItAll_Fails_ToWriteToDB()
{
[…]
}
DoItAllTests.cs
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19. Dependency Kata: Better Coverage
• Change the assert
Assert.That(doItAll.Do(),
Is.StringContaining("Database.SaveToLog Exception:”));
• Build will fail because our Do() method doesn’t return anything.
DoItAllTests.cs
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20. Dependency Kata: Better Coverage
• Change Do()’s return type to string
public string Do()
• Add/update return statements in 3 locations:
public string Do()
{
[…]
if (_userDetails.PasswordEncrypted […])
{
[…]
return string.Empty;
}
[…]
{
[…]
using (var writer = new StreamWriter("log.txt", true))
{
[…]
return string.Empty;
}
}
[…]
return string.Empty;
}
DoItAll.cs
DoItAll.cs
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21. Dependency Kata: Better Coverage
Now create variables to hold the messages to return
public string Do()
{
[…]
if (_userDetails.PasswordEncrypted […])
{
var passwordsDontMatch = "The passwords don't match.";
[…]
}
[…]
{
[…]
using (var writer = new StreamWriter("log.txt", true))
{
var errorMessage = $"{message} - Database.SaveToLog Exception: rn{ex.Message}";
[…]
}
}
[…]
}
DoItAll.cs
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22. Dependency Kata: Better Coverage
Return the new values as appropriate
public string Do()
{
[…]
if (_userDetails.PasswordEncrypted […])
{
var passwordsDontMatch = "The passwords don't match.";
Console.WriteLine(passwordsDontMatch);
_consoleAdapter.GetInput();
return passwordsDontMatch;
}
[…]
{
[…]
using (var writer = new StreamWriter("log.txt", true))
{
var errorMessage = $"{message} - Database.SaveToLog Exception: rn{ex.Message}";
writer.WriteLine(errorMessage);
return errorMessage;
}
}
}
DoItAll.cs
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23. Dependency Kata: Better Abstraction
Abstract Console completely by adding the following code:
• Add a new IConsoleAdapter method
void SetOutput(string output);
• Update ConsoleAdapter implementation
public void SetOutput(string output)
{
Console.WriteLine(output);
}
ConsoleAdapter.cs
ConsoleAdapter.cs
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24. Dependency Kata: More Abstraction
Update FakeConsoleAdapter implementation
public void SetOutput(string output)
{}
DoItAllTests.cs
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25. Dependency Kata: More Abstraction
• Update DoItAll Implementation
• Replace 5 instances of Console.WriteLine
WITH _consoleAdapter.SetOutput
• Replace 1 instance of Console.Write
WITH _consoleAdapter.SetOutput
DoItAll.cs
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26. Dependency Kata: Refactor
DoItAll.Do() is trying to do too much. Let’s Refactor!
Write a TEST
Logger.cs
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27. Dependency Kata: Refactor
DoItAll.Do() is trying to do too much. Let’s Refactor!
• Extract logging functionality by creating a new interface
public interface ILogger
{
string LogMessage(string message);
}
• Create a new class implementing ILogger
public class Logger : ILogger
{
public string LogMessage(string message)
{
throw new NotImplementedException();
}
}
Logger.cs
Logger.cs
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28. Dependency Kata: Refactor
• Copy the entire try/catch block in DoItAll.Do()
into the implementation of Logger.LogMessage()
• Modify var errorMessage to be outputMessage
• Make sure all paths return a outputMessage
public string LogMessage(string message)
{
var outputMessage = message;
[…]
return outputMessage;
}
Logger.cs
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29. Dependency Kata: Refactor
• Copy the entire try/catch block in DoItAll.Do()
into the implementation of Logger.LogMessage()
• Modify var errorMessage to be outputMessage
• Make sure all paths return a outputMessage
public string LogMessage(string message)
{
var outputMessage = message;
try
{
Database.SaveToLog(outputMessage);
}
catch (Exception ex)
{
// If database write fails, write to file
using (var writer = new StreamWriter("log.txt", true))
{
outputMessage = $"{message} - Database.SaveToLog Exception: rn{ex.Message}";
writer.WriteLine(message);
}
}
return outputMessage;
}
Logger.cs
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30. Dependency Kata: Refactor
• Update the constructor of DoItAll with an ILogger
private readonly ILogger _logger;
public DoItAll(IConsoleAdapter consoleAdapter, ILogger logger)
{
_consoleAdapter = consoleAdapter;
_logger = logger;
}
[…]
DoItAll.cs
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31. Dependency Kata: Refactor
• Update the Do() method
public string Do()
{
[…]
_consoleAdapter.SetOutput(message);
message = _logger.LogMessage(message);
_consoleAdapter.GetInput();
return message;
}
DoItAll.cs
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32. Dependency Kata: Refactor
We have broken instantiations of DoItAll
• Instantiate and pass in our new handler
var doItAll = new DoItAll(new ConsoleAdapter(), new Logger());
Program.cs
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33. Dependency Kata: Refactor
Let’s update BOTH tests.
• Create a new implementation of ILogger
public class DoItAllTests
{
[…]
var doItAll = new DoItAll(new FakeConsoleAdapter(), new
FakeLogger());
[…]
}
[…]
public class FakeLogger : ILogger
{
public string LogMessage(
string message)
{
return string.Empty;
}
}
DoItAllTests.cs
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34. Dependency Kata: Refactor
• Create a third test by copying the second test and rename the copy
DoItAll_Succeeds_WithFakeLogging
• Update the copied assert
Assert.That(doItAll.Do(), Is.EqualTo(string.Empty));
• Now change the second test DoItAll_DoesItAll_FailsToWriteToDB to be an integration
test by depending on Logger and it will pass as well
var doItAll = new DoItAll(new FakeConsoleAdapter(), new Logger());
DoItAllTests.cs
DoItAllTests.cs
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DoItAllTests.cs

35. Dependency Kata: What’s Next?
Remove static keyword from the Database class and use an interface and DI.
New test file.
With fake and with concrete.
New interface for UserDetails.
Extract password validation to UserDetails method: HasValidPassword
Extract class UserRegistrationCommunication for Messages to users.
Add IoC Container?
Add Isolation Framework (ala Moq)?
Show ReSharper/Rider common refactorings?

36. Dependency Kata: What’s Next?
There is still plenty to refactor in this legacy code.
• What would you do next?

37. William Munn
twitter - @dubmun
Github – dubmun
BLOG – http://dubmun.com
Resources
Working Effectively with Legacy Code, Michael Feathers
The Art Of Unit Testing, Roy Osherove
Clean Code, Robert C. Martin
Pragmatic Programmer, Dave Thomas & Andy Hunt
Refactoring, Martin Fowler
Legacy Code Kata – V3.0