Or ways to enhance coding enjoyment, productivity and, most of all,

preserve your sanity.

Nicolas ConnaultWeb developer

Moodle HQ

February 19th 2008

Unit testing

2

Lecture Outline

Introduction to Unit Testing

Development principles

Unit Test Frameworks

Unit tests for legacy code

Resources

3

Introduction to Unit Testing

Overview: Why write unit tests? Why not?

What are bugs?

What unit tests won't do for you

4

Introduction to Unit Testing

Why write Unit Tests?

Clean, bug-free, documented code Quality software: less complaints Coding simplicity: less stress

Why not?

Not enough time!

Overview

5

Introduction to Unit Testing

The less tests, the more bugs

The more bugs, the more complaints

The more complaints, the more stress

The more stress, the less tests we write

Overview

6

Introduction to Unit Testing

Can we write

bug-free code?

Overview

?

???

?

??

7

Introduction to Unit TestingOverview

What is a bug?

An unwanted feature (memory leak, feature creep etc.)

A "broken" feature

A misunderstood feature (by the client or the coder)

"It's not a bug, it’s a feature!"

8

Introduction to Unit TestingOverview

What Unit Tests don’t do:

Performance issues

Integration errors

User interface issues

9

Introduction to Unit TestingStatistics

15%

5%

80%

Look for bugs

Fix bugs

Write new code

According to some very reliable sources, programmers tend to spend over 80% of their working time looking for causes of bugs in existing code, 15% fixing these bugs, and 5% designing and developing new code. (source: N.Connault's astute observations, 2008).

10

Introduction to Unit TestingCollateral Damage

Code Library 1 Code Library 2

Identify Bug

Fix bug

Patch library 1

Test library 1

Result:Waste of time

NEW HIDDENBUG !!!

Dependencies

11

Introduction to Unit TestingSolution

Code Library 1 Code Library 2

Identify Bug

Fix bug

Patch libraries

Test alllibraries

Result: Better code

When all tests pass...

Dependencies

12

Coding principles

Coding principles

that apply to unit testing

...

13

Coding principles

If you don't know why

your modification fixed a bug,

Ignorance is the enemy

you're almost guaranteed

to be the creator of at least one new bug

14

Coding principles

Development and testing

are not separate tasks

Holistic development

15

Coding principles

The goal of programming is to reduce the

amount of repetitive work and the number of

simple decisions humans need to make.

Testing code is repetitive, and it is usually

simple. Tests should be automated.

Automation

16

Coding principles

Each unit test must test a single unit of code.

A unit of code is usually a simple function

or a simple method.

Isolation

Example of an overloaded function:

solveWorldHunger(money)

17

Coding principles

One unit test

must never affect another.

The order in which they are run

must be absolutely inconsequential

Independence

18

Coding principles

When you need new functionality,

first write a failing unit test,

then implement the new code.

Test-driven development

19

Coding principles

Never introduce bugs

in your unit tests.

Write them with the same rigour

as with your regular code.

Reliability

20

Coding principles

Write mock objects for: Objects whose behaviour is non-deterministic (news feed)

Objects that are complex/difficult to set up

Objects that are slow

Objects that have or are a User Interface

Objects whose behaviour is hard to trigger

Objects that haven't yet been implemented

Mock objects

21

Coding principles

NEVER, NEVER, NEVER

commit code

if any unit test fails

!!!

Golden Rule

22

Coding principles

Test boundary conditions as much

as is possible and reasonable,

including heavy load conditions.

Thoroughness

23

Coding principles

Don't write tests for code

that will obviously never fail

Prioritise

24

Questions and answers

?+!

25

Unit test Frameworks

Automate the generation of unit testing code

Simplify the entire process

Provide advanced testing features (mock

objects, fancy reports, expectations etc…)

Advantages

26

Unit Tests in legacy code

Too big a job to “catch up” all at once

Create unit tests to verify bug reports

Use unit tests to fix bugs

Refactor code when needed

Commit bug fix when all unit tests pass

27

Resources

Andrew Hunt and David Thomas. Pragmatic Unit Testing in Java with JUnit. The Pragmatic Programmers, LLC, Raleigh, NC, and Dallas, TX, 2004.

Venkat Subramaniam and Andy Hunt. Practices of an Agile Developer working in the Real World, The Pragmatic Bookshelf, 2006.

http://blog.daveastels.com/2005/07/05/a-new-look-at-test-driven-development

http://www.ibm.com/developerworks/java/library/j-cq09187/index.html

http://video.google.com/videoplay?docid=8135690990081075324