How to Start Test-Driven Development in Legacy Code

How to Start Test-Driven
Development in Legacy Code
The New York XP & Agile Meetup
May 17, 2012

Daniel Wellman
Director of Technology
Tweet
#legacytdd
#xpnyc

“red, green, refactor” by Török Gábor

Photo by the Dorothy Peyton Gray Transportation Library and Archive at the Los Angeles County Metropolitan
Transportation Authority

“Another ﬂaw in the human
character is that everybody
wants to build and nobody
wants to do
Kurt Vonnegut
maintenance.” Hocus Pocus

TDD Cycle

Red
Green
Refactor

Seams

Photo by Art Crimes a.k.a. Susan M. Coles

Legacy TDD Cycle

Introduce Seams
Red
Green
Refactor

Break dependencies
just enough
to get tests in place

Use Safe Refactoring
Tools
(if you have them)

Or move very slowly
and carefully

public class TestCase {

public void run() {
TestResult result = new TestResult();

try {
setUp();
runTest(result);
} catch (Exception e) {
result.addFailure(e, this);
}
tearDown();
}
}


public void run() {

try {
setUp();
runTest(result);
}
tearDown();
@Test
}
} public void exceptionsReportAsFailures() {
TestCase testCase = new TestCase();
testCase.run();
// ...??
}

After Extract Parameter

public void run(TestResult testResult) {
TestResult result = testResult;

try {
setUp();
runTest(result);
}
tearDown();
}
}

After Extract Parameter

public void run(TestResult testResult) {
TestResult result = testResult;

try {
setUp();
runTest(result);
@Test } catch (Exception e) {
public void exceptionsReportAsFailures() {
}
TestCase testCase = new TestCase();
tearDown();
} testCase.run(result);
} // Make assertions on result
}

The Dangerous
“Live Wire”

public class MailingListDispatcher {
private MailService mailService;

public MailingListDispatcher(Status status) {
this.mailService =
new SMTPMailService("smtp.gmail.com");
// ...
}

public Result send(Message message) {
// ...
mailService.send(message);
// ...
}
}


public MailingListDispatcher(Status status) {
this.mailService =
new SMTPMailService("smtp.gmail.com");
// ...
}

// ...
@Test
// ...
public void testSendSuccessful() {
} MailingListDispatcher dispatch =
} new MailingListDispatcher(OK);
dispatch.send(new Message());
// ... ???
}

After Parameterize Constructor

public MailingListDispatcher(
MailService service, Status status) {
this.mailService = service;
// ...
}

// ...
// ...
}

}

After Parameterize Constructor

public MailingListDispatcher(
MailService service, Status status) {
this.mailService = service;
// ...
}

@Test
public// ...
void testSendSuccessful() throws Exception {
MailService mailService = new FakeMailService();
MailingListDispatcher dispatch =
// ...
} new MailingListDispatcher(mailService, OK);
dispatch.send(new Message());
// Inspect the FakeMailService
} }

public class SMTPMailServer {
public void helo(String hostname) {}
public void from(String address) {}
public void size(long byteCount) {}
public void data() {}
public void send(Message message) {}
public void quit() {}
...

private int sendBytes(byte[] toSend) {}
...
}

Override Methods
public class FakeOverrideSMTPMailServer
extends SMTPMailServer {
public byte[] sent; // public!

@Override
protected int sendBytes(byte[] toSend) {
// Save the bytes for later inspection
// ...
return 0; // Whatever...
}
}

Override Methods
public class FakeOverrideSMTPMailServer
extends SMTPMailServer {
public byte[] sent; // public!

@Override
protected int sendBytes(byte[] toSend) {
// Save the bytes for later inspection
// ...
return 0; // Whatever...
public class SMTPMailServer {
}
} // ...
protected int sendBytes(byte[] toSend) { } ...

}

Extract Interface
public interface MailServer {
public void helo(String hostname);
public void send(Message message);
public void quit();
}

Extract Interface

sh
-i
public void quit();
}

Extract Interface

sh
-i
public void quit();
}

public class SMTPMailServer implements MailServer {
// Retro-fitted production...
}

Extract Interface

sh
-i
public void quit();
}

public class SMTPMailServer implements MailServer {
// Retro-fitted production...
}
public class FakeMailServer implements MailServer {
// Testing ...
}

public Duration vacationRemaining(Date today) {
Duration remaining;
// ...
// ...
// Calculate hours worked
// ...
// ...
// How much vacation do they get?
// ...
// ...
// Is it a leap year?
// ...
// ...
return remaining;
}

Extract Methods
public Time hoursWorked(Time start, Time end) {
// ...
}

public int vacationDaysAllowed(EmployeeType type) {
// ...
}

public boolean isLeapMonth(Date date) {
// ...
}

Sprout Method and
Sprout Class

“sprouting bean” photo by Zoë Jackson

public class EmployeeTable {
private List<Employee> employees;

public String table() {
StringBuilder html = new StringBuilder();
html.append("<table>");
for (Employee employee : employees) {
html.append("<tr>");
// Print employee data ...
html.append("</tr>");
}
html.append("</table>");
return html.toString();
}

}

public class EmployeeTable {

html.append("</tr>"); TODO:
} Show count
of full-time
} employees

}

Sprout Class
public class FullTimeEmployeeCount {

public FullTimeEmployeeCount(
List<Employee> employees) {
this.employees = employees;
}

public int count() {
int count = 0;
if (employee.isFullTime()) count++;
}
return count;
}
}

}

html.append("<td colspan='3'>");
html.append(
new FullTimeEmployeeCount(employees).count());
html.append("</td>");

}

12

9

6

3

0
Iteration 20 Iteration 21 Iteration 22 Iteration 23 Iteration 24

Velocity

What if
management
doesn’t think TDD is
valuable?

Any amount
is an improvement over
nothing

Many small steps
add up over time

Don’t be afraid to
delete and reshape

Upcoming Event
“How to Hire and Retain Developers”
by Debbie Madden, EVP
Monday @ 6 PM
General Assembly
http://generalassemb.ly/education/
More upcoming NYC and Boston Cyrus events at
http://www.cyrusinnovation.com/about/events

Questions?
Discussion!
Twitter: @wellman
E-mail: dwellman@cyrusinnovation.com

www.cyrusinnovation.com
Twitter: @cyrusinnovation

How to Start Test-Driven Development in Legacy Code

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (8)

Similar to How to Start Test-Driven Development in Legacy Code

Similar to How to Start Test-Driven Development in Legacy Code (20)

Recently uploaded

Recently uploaded (20)

How to Start Test-Driven Development in Legacy Code

Editor's Notes