Ten things you should know when writing good unit test cases

© 2013 IBM Corporation
Paul Thwaite IBM, Stuart Marks Oracle.
BOF 4255
Ten Things You Should Know
When Writing Good Unit Test
Cases in Java
Document number

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2

Who are we?
 Paul Thwaite
– QA Engineer, IBM
 Stuart Marks
– Principal Member of Technical Staff, Oracle

1. Think before you act
2. Make your tests understandable
3. Keep your tests “small and simple”
4. Test one thing only
5. Fast tests only
6. Absolute repeatability
7. Independent tests only
8. Provide diagnostic data on failure
9. No hard-coding of your
environment

5. Fast tests only
environment
What are you testing?
Why are you testing?
Plan

5. Fast tests only
environment
Comments
Expected behaviour
Aid debug
Diagnostics

5. Fast tests only
environment
Separate test logic / setup
Much easier to debug
Use setup / teardown

5. Fast tests only
environment
One scenario per test
Enables fast debug
Obvious why test failed

5. Fast tests only
environment
Run unit tests often as possible
Maintain quality bar
Quick results

5. Fast tests only
environment
Non-deterministic tests
are a headache
Fix intermittent tests immediately
No value, waste of resource
Must trust all tests

5. Fast tests only
environment
Must run in any order
Run subset, faster results
No dependencies

5. Fast tests only
environment
Use message in asserts
Make it simple to debug
Reference input data
Record test environment info

5. Fast tests only
environment
No ports, IP addresses,
data files, databases
Use config files, system
properties or mock objects
Portable tests

5. Fast tests only
environment
A passing test is a silent test
Too much output = confusion
Use option, config file to
turn on debug, save output

Over to you
 What are your experiences with unit testing ideals vs. real world?
 What testing problems and pathologies have you encountered?
 What are the root causes of your testing problems?
 What is the cost of test maintenance?

© 2013 IBM Corporation16
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Ten things you should know when writing good unit test cases

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