Test Driven Software Development Erik Zeitler Dream up

(Test Driven) Software Development Erik Zeitler

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 2021 -06 -12 Erik Zeitler 2

How to do it? § Think about the use cases • 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) 2021 -06 -12 Erik Zeitler 3

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 2021 -06 -12 Erik Zeitler 4

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 2021 -06 -12 Erik Zeitler 5

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 2021 -06 -12 Erik Zeitler 6

Example of an ER diagram 2021 -06 -12 Erik Zeitler 7

Why ER diagrams? § ”Keep talking about the algorithms, and everyone will stay totally mystified” § ”Show the ER diagram, and everything else will be obvious” 2021 -06 -12 Erik Zeitler 8

Software development is all about Getting Things Done Priorities • Make 2021 -06 -12 in software development: it work it beautiful it fast Erik Zeitler 9

How? 1. How to make it work? • First write tests, then write code. This is called Test Driven Development. 2. How to make it beautiful? • Re-factor 3. How to make it fast? • 2021 -06 -12 Don’t worry about performance until performance is a problem. Erik Zeitler 10

Why TDD? § Because • 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 2021 -06 -12 Erik Zeitler 11

The rules of TDD are simple 1. You can't write production code unless there is a broken test. • First write a test, then write the code 2. When there is a broken test, you change your code to make it pass. 3. When your code is working, you refactor to eliminate any code smells… 2021 -06 -12 Erik Zeitler 12

What is code smell? § ”Something is fishy about the code” § http: //en. wikipedia. org/wiki/Code_smell § 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 2021 -06 -12 Erik Zeitler 13

Demonstration yay 2021 -06 -12 Erik Zeitler 14

A good set of tests 1. Covers all code 1. How many lines of code do you have? 2. How many lines are tested? 3. Do you have > 90% test coverage? 2. performs tests on different scale 1. unit – integration – regression 3. tests for all cases, including edge cases and errors 1. e. g. expect. Exception() 2021 -06 -12 Erik Zeitler 15

Different sized tests isolation, speed 2021 -06 -12 Large (regression) Medium (integration) Small (unit) Erik Zeitler confidence in whole system 16

Where is the bug? vs. ”Test failed” 2021 -06 -12 Erik Zeitler 17

Does the entire system work? + vs. + + + 2021 -06 -12 Erik Zeitler 18

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%76 tr 423£ 4’, when they expected a single character (e. g. ’a’)? Generate exceptions in production code catch exceptions in test code 2021 -06 -12 Erik Zeitler 19

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 2021 -06 -12 Erik Zeitler 20

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 2021 -06 -12 Erik Zeitler 21