1.
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

2.
A Quick Survey

3.
“red, green, refactor” by Török Gábor

4.
Yay, TDD!

5.
Boo, my project!

6.
Get to Safety

7.
Be Persistent

8.
Photo by the Dorothy Peyton Gray Transportation Library and Archive at the Los Angeles County Metropolitan
Transportation Authority

9.
“Another flaw in the human
character is that everybody
wants to build and nobody
wants to do
Kurt Vonnegut
maintenance.” Hocus Pocus

10.
Photo by Fraser Speirs

11.
Get to Safety

12.
TDD Cycle
Red
Green
Refactor

13.
What makes code
hard to test?

14.
Highly Coupled Code

15.
Smaller Code

16.
How do I test this?

17.
Seams
Photo by Art Crimes a.k.a. Susan M. Coles

18.
Legacy TDD Cycle
Introduce Seams
Red
Green
Refactor

19.
??

20.
Break dependencies
just enough
to get tests in place

21.
Use Safe Refactoring
Tools
(if you have them)

22.
Or move very slowly
and carefully

23.
A Few
Techniques

24.
The Challenge of ‘new’

25.
public class TestCase {
public void run() {
TestResult result = new TestResult();
try {
setUp();
runTest(result);
} catch (Exception e) {
result.addFailure(e, this);
}
tearDown();
}
}

26.
public class TestCase {
public void run() {
TestResult result = new TestResult();
try {
setUp();
runTest(result);
} catch (Exception e) {
result.addFailure(e, this);
}
tearDown();
}
}

27.
public class TestCase {
public void run() {
TestResult result = new TestResult();
try {
setUp();
runTest(result);
} catch (Exception e) {
result.addFailure(e, this);
}
tearDown();
@Test
}
} public void exceptionsReportAsFailures() {
TestCase testCase = new TestCase();
testCase.run();
// ...??
}

28.
After Extract Parameter
public class TestCase {
public void run(TestResult testResult) {
TestResult result = testResult;
try {
setUp();
runTest(result);
} catch (Exception e) {
result.addFailure(e, this);
}
tearDown();
}
}

29.
After Extract Parameter
public class TestCase {
public void run(TestResult testResult) {
TestResult result = testResult;
try {
setUp();
runTest(result);
@Test } catch (Exception e) {
result.addFailure(e, this);
public void exceptionsReportAsFailures() {
}
TestCase testCase = new TestCase();
tearDown();
TestResult result = new TestResult();
} testCase.run(result);
} // Make assertions on result
}

30.
The Dangerous
“Live Wire”

31.
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);
// ...
}
}

32.
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);
@Test
// ...
public void testSendSuccessful() {
} MailingListDispatcher dispatch =
} new MailingListDispatcher(OK);
dispatch.send(new Message());
// ... ???
}

33.
After Parameterize Constructor
public class MailingListDispatcher {
private MailService mailService;
public MailingListDispatcher(
MailService service, Status status) {
this.mailService = service;
// ...
}
public Result send(Message message) {
// ...
mailService.send(message);
// ...
}
}

34.
After Parameterize Constructor
public class MailingListDispatcher {
private MailService mailService;
public MailingListDispatcher(
MailService service, Status status) {
this.mailService = service;
// ...
}
public Result send(Message message) {
@Test
public// ...
void testSendSuccessful() throws Exception {
MailService mailService = new FakeMailService();
mailService.send(message);
MailingListDispatcher dispatch =
// ...
} new MailingListDispatcher(mailService, OK);
dispatch.send(new Message());
// Inspect the FakeMailService
} }

35.
Can’t Make a Fake?

36.
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) {}
...
}

37.
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...
}
}

38.
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) { } ...
}

39.
Extract Interface
public interface MailServer {
public void helo(String hostname);
public void send(Message message);
public void quit();
}

40.
Extract Interface
sh
-i
public interface MailServer {
public void helo(String hostname);
public void send(Message message);
public void quit();
}

41.
Extract Interface
sh
-i
public interface MailServer {
public void helo(String hostname);
public void send(Message message);
public void quit();
}
public class SMTPMailServer implements MailServer {
// Retro-fitted production...
}

42.
Extract Interface
sh
-i
public interface MailServer {
public void helo(String hostname);
public void send(Message message);
public void quit();
}
public class SMTPMailServer implements MailServer {
// Retro-fitted production...
}
public class FakeMailServer implements MailServer {
// Testing ...
}

43.
Long Method?

44.
public Duration vacationRemaining(Date today) {
Duration remaining;
// ...
// ...
// Calculate hours worked
// ...
// ...
// How much vacation do they get?
// ...
// ...
// Is it a leap year?
// ...
// ...
return remaining;
}

45.
Extract Methods
public Time hoursWorked(Time start, Time end) {
// ...
}
public int vacationDaysAllowed(EmployeeType type) {
// ...
}
public boolean isLeapMonth(Date date) {
// ...
}

46.
Not much time to
change?

47.
Sprout Method and
Sprout Class
“sprouting bean” photo by Zoë Jackson

48.
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();
}
}

49.
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>"); TODO:
} Show count
html.append("</table>");
of full-time
return html.toString();
} employees
}

50.
Sprout Class
public class FullTimeEmployeeCount {
private List<Employee> employees;
public FullTimeEmployeeCount(
List<Employee> employees) {
this.employees = employees;
}
public int count() {
int count = 0;
for (Employee employee : employees) {
if (employee.isFullTime()) count++;
}
return count;
}
}

51.
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("<tr>");
html.append("<td colspan='3'>");
html.append(
new FullTimeEmployeeCount(employees).count());
html.append("</td>");
html.append("</tr>");
html.append("</table>");
return html.toString();
}

52.
Crazy
Third-Party API?

53.
You are
not alone

54.
Google

55.
End-to-End
Tests?

56.
Be Persistent

57.
It’s
going
to be
hard

58.
12
9
6
3
0
Iteration 20 Iteration 21 Iteration 22 Iteration 23 Iteration 24
Velocity

59.
What if
management
doesn’t think TDD is
valuable?

60.
Any amount
is an improvement over
nothing

61.
Many small steps
add up over time

62.
Do it every day

63.
Don’t be afraid to
delete and reshape

64.
Be Creative

65.
Pair Programming

66.
Spread experts around

67.
Get to Safety
Be Persistent

68.
Yay, TDD
on my project!

69.
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

70.
Questions?
Discussion!
Twitter: @wellman
E-mail: dwellman@cyrusinnovation.com
www.cyrusinnovation.com
Twitter: @cyrusinnovation