Testing, The Ugly Stepchild of Software Development

Better Living through Software Testing

Chris Berry – Feb 21, 2000

Chris Berry cberry@cyberplus.comChris Berry cberry@cyberplus.com

Why Test? It’s easy to fool yourself. Increase confidence. Increase productivity. Increase courage. It simply makes programming

more fun!

Test Early, Test Often Defects are order of magnitude

cheaper to fix when programmers find their own errors.

No communication cost. The bug tracking system does not

become involved. The error does not block or corrupt

the work of other developers.

Preemptive Testing The Art of catching bugs before

they happen. Defensive Programming. Programming by Contract.

The Assertion The hallmark of Defensive

Programming. Allows you to assert that a particular

condition is met, and commonly, if it is not, terminate execution.

Pre and post conditions. Not to be confused with Exceptions.

Sanity Checking A simple coding convention which

requires all Classes to provide a boolean isSane method.

Used to determine whether a particular Instance is in a sane state.

Logging/Debug Prints Low tech debugging technique.

Often the only way to debug threaded code.

Can speed development. Permanent artifact. Can result in “Scroll-blindness”. Best

to divert logging to a file rather than standard out.

The log4j package for Java.

Unit Testing Test each unit of code

independently. In OO, this equates to testing a

Class and its public interface. Involves debugging,

simultaneously, the code, the test, and the Spec.

Unit Testing is Glass Box Testing You Must be aware of

All branches of the method under test.

What inputs should produce what results or Exceptions.

The interplay of affected member variables and arguments.

Building a Good Unit Test Test for

Data integrity: Valid input: Insure that correct

outputs are generated for correct input conditions.

Invalid input: Insures proper error handling.

Deciding on Unit Test Input Equivalence Partitioning.

Good partitioning gives rigor without redundancy.

Boundary Analysis Things go wrong at the edges.

Expected and unexpected Exceptions.

Equivalence Partitioning An equivalence class is a definition

of a group of inputs, any one of which should be treated exactly the same by the method under test.

Eliminates redundant tests. The behavior of the method should be “equivalent” so only one test need be run for any equivalence class.

Boundary Analysis The term for choosing the

appropriate values to test a particular equivalence subset.

Choose values at the edge of the set.

Also a good idea to include the transition values.

Dealing with Exceptions Catch all unplanned Exceptions. Match all thrown Exceptions with

the conditions expected to produce them.

Classic Unit Test constructGenerate argument providersLoops over all argument providers Construct the Object under test (OUT) Optionally save the state of the OUT Call the method under test (MUT) If an exception was generated Test for unhandled exceptions Else Assertions on the resultant, OUT, and

argumentsEnd loops

Integration Testing Tests which prove that the

program properly executes some required functionality.

Typically involves the integration of many Classes.

Often a test from the perspective of the customer.

eXtreme Programming “A lightweight, low-risk, flexible,

predictable, and fun way to develop software”.

Takes commonsense best practices and applies them to an extreme degree.

XP in a Nutshell Code is king. Embrace change. Constant design. Emphasis on refactoring.

The Four Variables Cost Time Quality Scope.

The Four Values of XP Communication Simplicity Feedback Courage.

Central Principles of XP Rapid Feedback. Assume Simplicity. Incremental change. Embrace change. Quality work.

Secondary Principles of XP Teach Learning. Small Initial Investment. Play to Win. Concrete Experiments. Honest communication.

Secondary Principles of XP, continued Work with instincts. Accepted responsibility. Local adaptation. Travel Light. Honest measurement.

Four Basic Activities of XP Coding. Testing. Listening. Designing.

XP Development Practices On-site Customer System Metaphor Pair Programming Tests Before Code Simple Design

XP Development Practices, continued Merciless Refactoring Continuous Integration Collective Ownership Coding Standards

Testing the XP way A simplified, pragmatic, and less rigorous

approach to testing. Tests things that might break. Testing

simple methods, like accessors, is valueless. Write the tests first. Keep the tests running. Tests are automatic. Run the full suite

several times a day. JUnit, a Java testing framework. A C++

version (CPPUnit) is now available.

Summary The earlier you catch a bug the

less it is going to cost you. Testing can actually speed up your

development time, and improve your quality of life.

XP is a pragmatic approach to writing better software.

XP embraces change.

Acknowledgements Some of the Slide Notes for this

presentation were lifted verbatim from several sources; “Test Infected. Programmers Love Writing

Tests” by Eric Gamma and Kent Beck. “eXtreme Summary - An Overview of eXtreme

Programming eXplained: Embrace Change” by Brad Appleton.

“Divide and Conquer - Preemptive and Unit Testing” by Chris Berry

“The Pragmatic Programmer” by Andrew Hunt and David Thomas.

Resources www.xprogramming.com/software.

htm www.extremeprogramming.org www.pragmaticprogrammer.com