The document provides an introduction to test driven development (TDD). It discusses the benefits of TDD over traditional testing at the end such as ensuring no untested code is pushed to production. The TDD process of red-green-refactor is explained along with its three core rules. An example of building a string calculator using TDD is presented to demonstrate how to iteratively add features using a test-first approach.

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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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