A JavaOne BOF session on ten things you should know when writing good unit test cases. These ten simple rules will help guide developers to write solid unit tests which will be easy to run, debug and maintain.

1. © 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

2. © 2013 IBM Corporation
Important Disclaimers
THE INFORMATION CONTAINED IN THIS PRESENTATION IS PROVIDED FOR INFORMATIONAL PURPOSES ONLY.
WHILST EFFORTS WERE MADE TO VERIFY THE COMPLETENESS AND ACCURACY OF THE INFORMATION
CONTAINED IN THIS PRESENTATION, IT IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED.
ALL PERFORMANCE DATA INCLUDED IN THIS PRESENTATION HAVE BEEN GATHERED IN A CONTROLLED
ENVIRONMENT. YOUR OWN TEST RESULTS MAY VARY BASED ON HARDWARE, SOFTWARE OR
INFRASTRUCTURE DIFFERENCES.
ALL DATA INCLUDED IN THIS PRESENTATION ARE MEANT TO BE USED ONLY AS A GUIDE.
IN ADDITION, THE INFORMATION CONTAINED IN THIS PRESENTATION IS BASED ON IBM’S CURRENT PRODUCT
PLANS AND STRATEGY, WHICH ARE SUBJECT TO CHANGE BY IBM, WITHOUT NOTICE.
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2

3. © 2013 IBM Corporation
Who are we?
 Paul Thwaite
– QA Engineer, IBM
 Stuart Marks
– Principal Member of Technical Staff, Oracle

4. © 2013 IBM Corporation
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. © 2013 IBM Corporation
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
What are you testing?
Why are you testing?
Plan

6. © 2013 IBM Corporation
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
Comments
Expected behaviour
Aid debug
Diagnostics

7. © 2013 IBM Corporation
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
Separate test logic / setup
Much easier to debug
Use setup / teardown

8. © 2013 IBM Corporation
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
One scenario per test
Enables fast debug
Obvious why test failed

9. © 2013 IBM Corporation
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
Run unit tests often as possible
Maintain quality bar
Quick results

10. © 2013 IBM Corporation
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
Non-deterministic tests
are a headache
Fix intermittent tests immediately
No value, waste of resource
Must trust all tests

11. © 2013 IBM Corporation
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
Must run in any order
Run subset, faster results
No dependencies

12. © 2013 IBM Corporation
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
Use message in asserts
Make it simple to debug
Reference input data
Record test environment info

13. © 2013 IBM Corporation
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
No ports, IP addresses,
data files, databases
Use config files, system
properties or mock objects
Portable tests

14. © 2013 IBM Corporation
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
A passing test is a silent test
Too much output = confusion
Use option, config file to
turn on debug, save output

15. © 2013 IBM Corporation
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?

16. © 2013 IBM Corporation16
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