Adding Unit Test To Legacy Code
description
Some experience sharing about adding unit test to legacy code in large embedded system.
Transcript of Adding Unit Test To Legacy Code
AgendaBackgroundMotivationPrinciplesPracticesWhat is fun?
BACKGROUND
Large scale software Telecommunication device10+ years old1,000 people10,000,000 lines of code in one buildC, SDLSome very complicatedThousands LOCs functionsCyclomatic complexity > 50.Duplicate rate > 100%!
Where do we usually call it legacy code?
MOTIVATION
It's NOT about finding bugs!The purpose of unit testing is to facilitate changes
not to do it.You still have the choice and reasons
PRINCIPLES
BASIC UNIT TESTING PRINCIPLES
PRINCIPLE 1KEEP IT VERY SIMPLE, VERY STUPID
It is not that the more test cases the betterActually, it is on the contrary, the less the better. The purpose of UT is to facilitate change
It can only facilitate change if it surviveTherefore, it needs maintainabilitySo, it needs to be simple
"The only way for humans to deal with complexity is to avoid it ..."
PRINCIPLE 2 DON'T TRY TO ADD GOOD UT TO BAD CODE
PRINCIPLE 3DON'T MAKE ASSUMPTION
error_t release_message_received( msg_header_t * msg ) { DO_FAIL_TEXT("I'm called!!"); return SUCCESS_EC;}
Exploding stub
PRINCIPLE 4 STOP MAKING 'LEGACY CODE'
Test drive new codeAdd tests to legacy code before modificationTest drive changes to legacy code
Boy Scout Principle
PRINCIPLE 5EDUCATE THE PEOPLE
Do NOT let just one or two people do it.NEVER let interns do it!
WHERE TO START?
Setup the frameworkTo setup the framework for legacy code can be very challenging.Choose the test frameworkWe use CppUTest Ask for performance
Domain ModelingReverse engineering to clarify the concepts used in the legacy code
And their relationshipsUse the terms consistently in your unit testing.It will also give your refactoring a road-map.
Identify the hot areaStart from the hot area will be most cost-efficientExample
Through SVN logAlong with the new work and bug fixing
Bottom-up?Have some integration test firstThen,
One practical approach is bottom-upGet a higher level of abstraction
Learn the function by testing it
Characterization TestStart from the 1st (failing) exitWrite your plan on a piece of paper
Make the legacy code testable
Use safe refactoring techniques to change the legacy code without unit testing.
Extract functionIf you are using C
‘Data injection’ to break the dependency on globals.
Break Dependency
WHAT IS FUN
Bring chaos to orderLearn the featureDelete tons of codeFeel the peace of your heart
REFERENCES
Acknowledgement
