Program testing can be used to show the presence of bugs, but never to show their absence!
~ Edsger Dijkstra
Dijkstra, E. W. (1970). Notes on structured programming.
Retrieved September 4, 2007, from http://www.cs.utexas.edu/users/EWD/ewd02xx/EWD249.PDF

Microsoft … we have as many testers as we have developers. And testers spend all their time testing, and developers spend half their time testing. We're more of a testing, a quality software organization than we're a software organization.
~ Bill Gates
Foley, J. & Murphy, C. (2002). Q&A: Bill Gates on trustworthy computing . InformationWeek.
Retrieved September 4, 2007, from http://www.informationweek.com/story/IWK20020517S0011

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Tests reduce bugs in new features
Tests reduce bugs in existing features
Tests are good documentation
Tests reduce the cost of change
Tests improve design
Tests allow refactoring
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Tests constrain features
Tests defend against other programmers
Testing is fun
Testing forces you to slow down and think
Testing makes development faster
Tests reduce fear
Burke, E.M. & Coyner, B.M. (2003). Top 12 reasons to write unit tests.
Retrieved September 1, 2007, from http://www.onjava.com/pub/a/onjava/2003/04/02/javaxpckbk.html

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Informal definition -- a test case is a piece of code that programmatically checks that another piece of code works correctly
Each test case is a method that usually tests another method (often called the
“method under test”)

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Positive test cases test that the method under test works correctly with expected, legitimate inputs
 “happy path”
 Test for success
Boundary test cases test how the method under test handles values that lie at the boundary of acceptable inputs
 Legal values that often cause problems in code
 zero, empty strings, null object references
Negative test cases try to show that the method under test does not work or that the method under test handles error conditions
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Open-ended
Test for failure
Horstmann, C. (2008). Big Java (3 rd ed.). New York: John Wiley & Sons.

 Black-box testing describes a testing method that does not take the structure of the implementation into account
 Based on what is externally visible (inputs and expected outputs)
 White-box testing uses information about the structure of a program
 Based on implementation details
Horstmann, C. (2008). Big Java (3 rd ed.). New York: John Wiley & Sons.

 Regression testing
 Repeating previously run tests to ensure that known failures of prior versions do not appear in the new versions of the software
 Test coverage
 Every line of executable code should be executed at least once by test cases
 Every if / else branch
 All paths through your code
Horstmann, C. (2008). Big Java (3 rd ed.). New York: John Wiley & Sons.

Question: How many test cases do you need to cover all branches of the getDescription method shown below?
What are the boundaries?
public String getDescription()
{
String r; if (richter >= 8.0) r = “Most structures fall”; else if (richter >= 7.0) r = “Many buildings destroyed”; else if (richter >= 6.0) r = “Many buildings considerably damaged, some collapse”; else if (richter >= 4.5) r = “Damage to poorly constructed buildings”; else if (richter >= 3.5) r = “Felt by many people, no destruction”; else if (richter >= 0) r = “Generally not felt by people”; else r = “Negative numbers are not valid”; return r;
} private double richter;
Horstmann, C. (2008). Big Java (3 rd ed.). New York: John Wiley & Sons.

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BlueJ allows for ad hoc and systematic unit testing
 Ad hoc testing allows you to test a method interactively
 Systematic testing is done using the JUnit regression testing framework
 BlueJ can be used to generate test cases or to build test cases by hand
When you installed BlueJ, it should have included a tutorial on testing which also can be downloaded from: http://www.bluej.org/tutorial/testing-tutorial.pdf

 Informal definition -- debugging is the process of finding and fixing problems
(bugs) in a computer program or in computer hardware

Department of the Navy. (2006). Online library of selected images: Rear Admiral Grace Murray
Hopper, USNR, (1906-1992). Retrieved September 4, 2007, from http://www.history.navy.mil/photos/pers-us/uspers-h/g-hoppr.htm

 Reproduce the error
 Simplify the error
 Divide and conquer
 Know what your program should do
 Look at all details
 Make sure you understand each bug before you fix it
Horstmann, C. (2008). Big Java (3 rd ed.). New York: John Wiley & Sons.

 A debugger is a program that you can use to execute another program and analyze its run-time behavior
 Basic debugger functions:
 Setting breakpoints
 Stepping through code
 Inspecting variables
Horstmann, C. (2008). Big Java (3 rd ed.). New York: John Wiley & Sons.

 A simple debugger is included in the BlueJ development environment
 Learning to use it can save you lots of time
 When you installed BlueJ, it should have included a tutorial which also can be downloaded from: http://www.bluej.org/tutorial/tutorial.pdf
 Debugger demonstration is on pages 27-30

 An ITiCSE working group created a repository of debugging video tutorials that demonstrate some debugging techniques, including how to use the BlueJ debugger http://debug.csi.muohio.edu/

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Testing is an important part of software development
Test cases can be used to develop code, find bugs, and make sure changes don’t break old code
Test cases should provide full coverage, test the inputs and expected outputs, test boundaries, etc.
JUnit is a framework used to develop test cases
BlueJ supports JUnit test cases and also includes a debugger to help fix problems found in code