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Introduction
to
Test Driven
Development
(TDD)

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Introductions!
1.Your Name
2.Current company & Role
3.Experience with Agile and TDD

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Agile Software Development

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Traditional Design – Code – Test
Design Code Test
Test Code
Design /
Refactor

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Why Not Testing at the End?
• Hard to improve quality of
existing code –
Complacency and Recency
• Feedback opportunity is
lost
• The future state of the
project is difficult to gauge
• Testing is more likely to be
cut

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Stress and Testing
Project
Stress
Less
Testing
Just get it done, will ya?

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Test Automation Pyramid
UI
Service
Unit
UI
Service
Unit
AgileTraditional

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Test First Development
ATDD and TDD

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ATDD vs TDD
Source: Test Driven: Practical TDD and Acceptance TDD for Java Developers

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Why TDD?
The Benefits of TDD:
• Limits WIP – a key Lean principle
• Ensures testing at lower granularity level – the smallest
testable unit of code
• Ensures no untested code goes to production
• Helps high degree of conformity between code and the
real business requirements
• Helps keep unused code out of the system (unwritten)
• Makes codebase more maintainable – via regression
testing

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The TDD Cycle
 Red
 Green
 Clean
Test
Code
Refactor

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Three Laws/ Rules of TDD
You will not write any production
code until you have written a failing
unit test.
First Law

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Three laws of TDD
You will not write more of a unit
test than is sufficient to fail, and
not compiling is failing
Second Law

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Three laws of TDD
You will not write more production
code that is sufficient to pass the
currently failing test.
Third Law

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Misconceptions About TDD
• Writing code first, then tests is
same as TDD
• TDD isn’t useful for designing
architecture
• Takes too much time
• Too complex to learn and
implement
• TDD is only good for small
projects

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Let’s Build Something Now!

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String Calculator – TDD Exercise
Define Scope:
• Supported operators?
• Acceptable characters?
• Whitespace?
• Max length of expression – number of operations?
• Max length of each number?
• Fractions?
• Parenthesis?

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String Calculator (continued)
Time to start Failing!
• Reminders:
• Test, Code, Refactor – REPEAT until Done!
• Add feature layers one by one, in small manageable
increments
• Setup
• Eclipse for Java Development
• JDK
• Team formation

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String Calculator (continued)
1. Two literal addition
A + B

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String Calculator (continued)
2. Multiple literal addition
A + B + C
A + B + C + D

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String Calculator (continued)
3. Combination of addition and
subtraction
A + B – C
or
A – B + C

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String Calculator (continued)
4. Simple multiplication
A * B
A * B * C

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String Calculator (continued)
5. Simple division
A / B
A / B / C

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String Calculator (continued)
6. Combination of multiplication
and division
A * B / C
A / B * C
Does order matter?

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String Calculator (continued)
7. Combination of all four
A + B – C * D / E
Order does matter here!

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String Calculator (continued)
8. Invalid expressions
• Banned chars - alpha, parenthesis, special chars
• Space between a number
• Two operators clubbed together
• First number negative
• Invalid decimal number

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What Next?
Certified Scrum Developer (CSD)
A 3-day course certified by Scrum Alliance that focuses on
specialized Agile engineering skills:
 Test Driven Development (TDD)
 ATDD, BDD – Selenium/ Cucumber
 Continuous Integration – Jenkins
 Agile Design and Architecture
 Refactoring
 Collaboration

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References
 Test Driven Development: By Example - Kent Beck
 Succeeding with Agile - Mike Cohn
 Test Driven: Practical TDD and Acceptance TDD for Java
Developers - Lasse Koskela

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