1. (Test Driven) Software Development
11/16/2018
(Test Driven) Software Development
Erik Zeitler

2. Dream up a business case
Think of a service you want to see
Figure out how to do it in a way that doesn’t suck
Do it
Erik Zeitler

3. How to do it? Think about the use cases Cut the work into pieces
How will the service be used
Cut the work into pieces
User Interface, application code, database
Assign pieces within the project group
Use Test Driven Development
Test each piece (unit tests)
Test all pieces together (integration/regression tests)
Erik Zeitler

4. Rapid prototyping Make a simple prototype ASAP
See what new ideas it gives you
”Often, users don’t know what they want until they see it” – Steve Jobs
Show your prototype to the other project groups
Give feedback to each other
Erik Zeitler

5. Three-tier architecture
User Interface
What should the user see?
Make drawings
Database
What information will you keep?
Do data modelling, using ER diagrams
Business logic
How will you present the data to the users?
For any non-trivial function, do test driven development
Erik Zeitler

6. Data modelling Keep persistent data in a database
Customer information
Banking information
Inventory
What do you carry, and how much do you have right now?
Past activity
What has the customer bought?
What has the customer looked at?
What information do you want to store? Why?
Make an Entity Relationship diagram
Translate the ER diagram into SQL tables
Erik Zeitler

7. Example of an ER diagram
Erik Zeitler

8. Why ER diagrams?
”Keep talking about the algorithms, and everyone will stay totally mystified”
”Show the ER diagram, and everything else will be obvious”
Erik Zeitler

9. Software development is all about Getting Things Done
Priorities in software development:
Make it work
Make it beautiful
Make it fast
Erik Zeitler

10. How? How to make it work? How to make it beautiful?
First write tests,
then write code.
This is called Test Driven Development.
How to make it beautiful?
Re-factor
How to make it fast?
Don’t worry about performance until performance is a problem.
Erik Zeitler

11. Why TDD? Because Because does it A test is a specification
Debugging sucks
Testing rocks
Because does it
A test is a specification
The capabilities of a program is defined by its tests
If the tests pass
we know that the program works – for the test cases.
A test is a piece of documentation
Erik Zeitler

12. The rules of TDD are simple
You can't write production code unless there is a broken test.
First write a test, then write the code
When there is a broken test, you change your code to make it pass.
When your code is working, you refactor to eliminate any code smells…
Erik Zeitler

13. What is code smell? ”Something is fishy about the code”
Examples:
Large method
A function that is > 1 page
Duplicated method
A method, function, or procedure that is very similar to another.
Contrived Complexity
Forced usage of overly complicated design patterns where simpler design would suffice
Erik Zeitler

14. Demonstration
yay
Erik Zeitler

15. A good set of tests Covers all code performs tests on different scale
How many lines of code do you have?
How many lines are tested?
Do you have > 90% test coverage?
performs tests on different scale
unit – integration – regression
tests for all cases, including edge cases and errors
e.g. expectException()
Erik Zeitler

16. Different sized tests Large (regression) Medium (integration) Small
(unit)
isolation, speed
confidence in whole system
Erik Zeitler

17. Where is the bug? vs. ”Test failed” ”Test failed” 2018-11-16
Erik Zeitler

18. Does the entire system work?+
vs. + + +
Erik Zeitler

19. Tests for edge cases and errors
Write tests for invalid input data, like
empty strings
empty data sets
false
broken input data
what happens to your functions if they get ’a%76tr423£4’, when they expected a single character (e.g. ’a’)?
Generate exceptions in production code
catch exceptions in test code
Erik Zeitler

20. Test your database
Set up a test database, identical to your production database
Grant privileges to your php test script
Call your stored procedures from your php test script
Validate the result data from the database
Erik Zeitler

21. Further resources Soon available on the course home page:
The latest PHPUnit (simpletest)
These slides
My demonstration examples
IDEs (Eclipse, Netbeans, ...) have infrastructure for testing
Erik Zeitler