Test Driven Development is nothing more than "Unit Testing" but an art of unit testing. Arts require lots of practice. To start with TDD, it is very important to understand what is unit testing. The common problem many coders have is "Not understanding what is a unit". This presentation targets to solve this basic problem than going behind non-understandable jargons.

1. TDD
The Art of Fearless Programming
On 06/23/2016 @ SLASSCOM Quality Forum
BY CHAMIL JEEWANTHA
SOFTWARE ARCHITECT AT ZONE24X7
ALL RIGHTS RESERVED

2. What Will You Take Back?
 Test Driven Development
 Answers for What? Why? Who? When? & Where?
 Better understanding of a ”Unit”?
 The difference between,
 Unit Test, Integration Test, Test First Development, ATDD
 Your belongings ;)

3. Some Groundwork
 Ask questions
 Art vs Science
 Arts require lots of practice
 Arts do not require to be proven
 Overlaps may occur
 Most of the points are subjective
 E.g. Drinking water is good (in general, not always)

4. Pitch Report ARE WE ON THE SAME
PAGE?

5. Some Core Values
 Quality is everyone’s responsibility
 Good test coverage is important
 Line coverage != test coverage
 Early testing is better
 More test cycles are better
 Architecture plays a big role in Maintainability
 Maintainability is a significant Quality aspect (Specially with Agile)

6. What is Unit Testing?
 A single, indivisible entity
 The smallest testable part of an application
 End User  Entire software
 QA Engineer  Single Functionality
 Architect  A Module, Component
 Developer  A Class (OOP), Function (FP)

7. Class? Why not Method (OOP)?
IF
A class follows the “Single Responsibility Principle”
AND
The methods are cohesive
THEN
Really hard to use a method independently

8. A Unit for a Politician
Source: https://en.wikipedia.org/wiki/William_Bennett

9. “
”
If we have stronger families we will
have stronger schools and stronger
communities with less poverty and less
crime.
WILLIAM BENNETT, A FORMER UNITED STATES SECRETARY OF EDUCATION
http://www.nytimes.com/roomfordebate/2012/04/24/are-
family-values-outdated/stronger-families-stronger-societies

10. “
”
If we have stronger Units we will have
stronger Modules and stronger
Software with Rich Features and less
Bugs.
CHAMIL JEEWANTHA, SOFTWARE ARCHITECT @ ZONE24X7
TDD (The Art of Fearless Programming) - SLASSCOM Quality
Forum

11. Example of a Unit
public class AndCriteria implements Criteria{
private final Criteria criteria1;
private final Criteria criteria2;
public AndCriteria(Criteria criteria1, Criteria criteria2) {
this.criteria1 = criteria1;
this.criteria2 = criteria2;
}
public List filter(List values) {
List filteredList = criteria1.filter(values);
return criteria2.filter(filteredList);
}
}

12. Characteristics of a Good Unit
 Not so lengthy
 Self explained
 Used by its clients via an interface
 SOLID
 Well Tested
 Compliant with Best Practices (All above + many
more)

13. Unit Test
 Select the smallest piece of testable software in the
application
 Isolate it from the rest of the code
 Determine whether it behaves exactly as you expect
 Each unit is tested separately before integrating them into
modules to test the interfaces between modules
 Ref: https://msdn.microsoft.com/en-
us/library/aa292197(VS.71).aspx

14. Characteristics of a Good Unit Test
 Automated
 Thorough
 Repeatable
 Independent
 Test only one thing
 Should not rely on each other
 Fast
 Professional (Readable, Maintainable, Trustworthy)

15. Isolating a Unit for Testing
Is this Site
Manager good?
Site Manager
He should by
cement from the
shop named by me

16. Test Flow

17. How to Test
 Create a dummy bag of cement
 Create a dummy hardware shop
 Instruct the dummy hardware to send the dummy bag of
cement if somebody asks for a bag of cement.
 Give the address of dummy hardware to the site manager.
 Ask for a bag of cement from the site manager
 Verify whether he has called the given hardware
 Verify whether we receive the dummy cement bag back.

18. In Java with Mockito
BagOfCement dummyCement = mock(BagOfCement.class);
HwShop dummyHw = mock(HwShop.class);
When(dummyHw.buyCement()).thenReturn(dummyCement);
siteManager.setHwShop(dummyHw);
BagOfCement output = siteManager.askCement();
assertThat(output, is(dummyCement));
verify(dummyHw).buyCement();

19. Example: Requirement of
AndCriteria
 The AndCriteria should be an implementation of
Criteria
 Should filter a given list by first expression and return
a filteredList
 Should filter the filteredList by the second expression
and return the finalList

20. Example: Tests for AndCriteria
1. Should_FilterThrough1StAnd2ndExpressions_When_ALi
stIsGiven
2. Should_ThrowException_When_NullIsProvided

21. Example: AndCriteria : Test 1
@Test
public void Should_FilterThrough1StAnd2ndExpressions_When_AListIsGiven(){
List input = // dummy list
List lst1 = // dummy list
List lst2 = // dummy list
Criteria expr1 = // dummy criteria -> filter(input) returns dummy list (lst1)
Criteria expr2 = // dummy criteria -> filter(lst1) returns dummy list (lst2)
AndCriteria criteria = new AndCriteria(expr1, expr2);
List output = criteria.filter(input);
assertThat(output, is(lst2));
}

22. Example: AndCriteria : Test 2
@Test (expected = IllegalArgumentException.class)
public void Should_ThrowException_When_NullIsProvided() {
List input = null
AndCriteria criteria = new AndCriteria(expr1, expr2);
criteria.filter(input);
}

23. Example 2: Evaluate Expression
 The user should provide an expression with relevant
value mappings to its variables.
 Java Evaluate ((a+b)*3)-2 a=5 b=8
 The program should assign a & b values to this
expression and evaluate it.

24. Code for Evaluating an Expression
class Evaluate{
public static void main(String[] args){
String expr = ... // assign variables with values
// evaluate the expr
double value = // the output value of the evaluation
System.out.println(value);
}
}
Can you write a
“Good” automated
test?

25. Common Complaints About Unit
Testing
 Deadline is near, no time to write tests
 Writing tests takes longer than the production code
 Hard to keep the test suite up to date
 One line of code change breaks 100s of tests
The code
works. But
very hard to
write unit
tests
So, Refactor
your code
Not Hard,
Impossible!

26. Solution: (TFD)
Test First
Development
THE PARADIGM SHIFT

27. Rules: TFD
1. Write a(nother) unit test that fails
2. Write the minimum production code until all the tests
pass
3. Repeat until all your work is done.
Fail Pass

28. Test First Benefits (Vs Test Late)
All the benefits of Unit testing
+
 Write non-testable codes are impossible
 Test-first forces you to plan before you code
 It’s faster than writing code without tests
 It saves you from lengthy code
 It guides you to build good, SOLID units
 It increases your confidence (refactor without fear)
 Acts as a real-time progress bar

29. “
”
TDD = TFD + Refactoring
REFACTOR YOUR CODE AT EVERY ITERATION
TDD = Test Driven Development
TFD = Test First Development

30. Rules: TDD
1. Write a(nother) unit test that fails
2. Write the minimum production code until all the
tests pass
3. Refactor your code
4. Repeat until all your work is done
Fail Pass
Refactor

31. DEMO GET YOUR HANDS DIRTY
WITH TDD

32. Scenario
 For a given Access log file of a web server
 Client needs a command line utility to get
 Percentage of success responses
 Percentage of failure responses
Time Source Destination Response time Status
2016/04/22 12:15:05 PM 10.1.5.8 10.1.24.14 55 200

33. Approaching with TDD
 A Class called “LogAnalyzer”
 With method “analyze”
 Writing the analyze method
 Reading the file is not matching to this name
 Separate LogReader should be used
 LogReader.read should return List<Request>
 Two Stats to be calculated
 StatCalculator interface
 List of StatCalculators should be injected to LogAnalyzer

34. Tools
 IDE (IntelliJ)
 Test Runner (Junit)
 Mock libraries (Mockito)
 Verification (Hamcrest)

35. FAQ

36. ATDD vs TDD
 TDD to drive the design
 ATDD to make sure all the requirements are implemented

37. Additional time due to TDD?
 Beginner
 Lots of time thinking where to start
 Experienced Developer
 Initially 15 - 17% more
 Big time saving later for both

38. Thank You!
KDCHAMIL@GMAIL.COM