Lecture 9: Debugging & Testing

9-2 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Objectives “Unfortunately, errors are a part of life. Some are detected by the compiler, some are detected through testing, and the remainder go uncaught. Modern languages and tools like J#, Visual Studio.NET, and NUnit provide many techniques for quickly identifying, dealing with, and eliminating errors. But you have to apply them…” Debugging options Testing Testing with NUnit

9-3 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Part 1 Debugging options…

9-4 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Print debugging Everyone understands print debugging In.NET, you have various options: –console app: System.out.println(...); –GUI app: System.Windows.Forms.MessageBox.Show(...); –inside VS: System.Diagnostics.Debug.WriteLine(...);

9-5 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Source-level debugging Most development environments supply a debugger –allow you to debug your program line-by-line, look at vars, etc. –Visual Studio.NET contains a very sophisticated debugger Basic idea: –you set a breakpoint to pause your program at a certain point –run program in order to reach breakpoint –once paused, you can look at variables, single-step, etc. click in margin to set breakpoint

9-6 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Debug menu Once you reach breakpoint, you can: –single-step –view local vars –change values Example: –Watch window let’s you expand & inspect objects! See Debug menu for things you can do…

9-7 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Examples When using constructors, set a breakpoint where you do “ new Class1(…) ”, run to hit breakpoint, and then single-step, showing how constructor is automatically called… When using dynamic binding, single-step through calls to see how different method implementations are called dynamically…

9-8 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Part 2 Testing…

9-9 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Testing Good testing is a skill that students must develop: –algorithm boundary cases –single calls & sequences of calls –parameter validation –exception handling –etc. Good testing is automated –so there’s no reason not to do it Good testing is repeatable ( regression testing ) –so you can retest after any change to the code

9-10 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Basic testing methodology For every class C, create a test harness TC to test it –TC = one or more methods that exercise C Test harness should: –exercise all fields & methods in C –strive for 100% code coverage (exercise all paths of execution) –generate no output other than a final testing summary i.e. test harness should *not* rely on user to determine correctness user will forget what the “correct” output should be… class C test harness TC

9-11 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Example StudentsIO class reads student info from a file –returns an ArrayList of Student objects… public class StudentsIO { /** * Reads student info from given file, returning arraylist */ public static java.util.ArrayList read(String filename)... { java.util.ArrayList students; students = new java.util.ArrayList();. return students; } public class StudentsIO { /** * Reads student info from given file, returning arraylist */ public static java.util.ArrayList read(String filename)... { java.util.ArrayList students; students = new java.util.ArrayList();. return students; }

9-12 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Example test harness Tests StudentsIO.read( ) against various input files… public class StudentsIOTest { // tests against an empty input file… public static void readEmpty() throws java.lang.Exception { java.util.ArrayList students; students = StudentsIO.read("empty.txt"); if (students == null || students.size() != 0) throw new java.lang.Exception("readEmpty failed!"); } // tests against an input file with one student, "Jim Bag" public static void readOne() throws java.lang.Exception { java.util.ArrayList students; students = StudentsIO.read("one.txt");. public class StudentsIOTest { // tests against an empty input file… public static void readEmpty() throws java.lang.Exception { java.util.ArrayList students; students = StudentsIO.read("empty.txt"); if (students == null || students.size() != 0) throw new java.lang.Exception("readEmpty failed!"); } // tests against an input file with one student, "Jim Bag" public static void readOne() throws java.lang.Exception { java.util.ArrayList students; students = StudentsIO.read("one.txt");.

9-13 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Running test harness Common approach is to define a main method in test harness –Reconfigure VS to startup app using this main. Right-click on project in Solution Explorer (or use Project menu), select Properties, then Common Properties, then General, and set "Startup Object" in this case to "StudentApp.StudentsIOTest". public class StudentsIOTest { … public static void main(String[] args) { int failed = 0; System.out.println("** Testing StudentsIO **"); try { readEmpty(); } catch(Exception ex) { System.out.println(ex.toString()); failed++; } … } } //class public class StudentsIOTest { … public static void main(String[] args) { int failed = 0; System.out.println("** Testing StudentsIO **"); try { readEmpty(); } catch(Exception ex) { System.out.println(ex.toString()); failed++; } … } } //class

9-14 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Part 3 Testing with NUnit…

9-15 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET NUnit NUnit is based on the highly-successful Java tool JUnit –NUnit is for.NET code –NUnit is for testing "units", i.e. classes –available for free from

9-16 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET NUnit methodology NUnit automates the running of the test harness –it doesn't write the test harness for you (that's our job) –it runs the test harness & collects statistics….EXE /.DLL

9-17 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET How does NUnit help? NUnit helps in many ways: –you don't have to write the code to collect & output statistics –tells you exactly which tests failed / skipped –catches exceptions that testing methods may throw –provides a framework for regression testing, i.e. re-testing after source code has been modified

9-18 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Using NUnit Five-step process: 1.Download & install NUnit 2.Create test harness, with instance test methods & no main( ) 3.Set a reference to NUnit: Project menu, Add Reference… Browse… Navigate to C:\Program Files\NUnit V2.1\bin Open "nunit.framework.dll" Ok 4.Add NUnit attributes to test harness, rebuild project 5.Startup Nunit-Gui via Start menu, open compiled code, & run! "Green" light means test passed "Yellow" light means test was skipped "Red" light means test failed

9-19 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Example Let's revisit test harness for StudentsIO.read( )… Same as before, except: –no main method; test methods should be instance methods –addition of NUnit attributes to identify test harness & methods NUnit.Framework.TestFixture() */ public class StudentsIOTest { NUnit.Framework.Test() */ public void readEmpty() throws java.lang.Exception { java.util.ArrayList students; students = StudentsIO.read("empty.txt"); if (students == null || students.size() != 0) throw new java.lang.Exception("readEmpty failed!"); }. NUnit.Framework.TestFixture() */ public class StudentsIOTest { NUnit.Framework.Test() */ public void readEmpty() throws java.lang.Exception { java.util.ArrayList students; students = StudentsIO.read("empty.txt"); if (students == null || students.size() != 0) throw new java.lang.Exception("readEmpty failed!"); }.

9-20 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Working with NUnit Idea: –compile test harness, etc. in Visual Studio.NET –startup Nunit-Gui, file >> open compiled code, run test harness Green is good, Yellow is caution, Red is bad –leave both tools open, compiling in VS & testing in NUnit.EXE /.DLL

9-21 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Debugging with NUnit Visual Studio's debugger is still available Process for debugging: –open Visual Studio & Nunit-Gui as usual –set breakpoints in VS as usual –in VS, attach debugger to Nunit-Gui as follows: Debug menu Processes… select "nunit-gui.exe" from list click "Attach" check the box for "Common Language Runtime" & click OK close Processes window, notice that VS is now in "Run" mode –in Nunit-Gui, click Run button! when you are done testing/debugging, you'll need to stop VS…

9-22 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Writing a test method If test method returns, counted as success If test method throws an exception, counted as failure Implication: –test method must throw an exception to denote failed test… NUnit.Framework.Test() */ public void readEmpty() throws java.lang.Exception { java.util.ArrayList students; students = StudentsIO.read("empty.txt"); if (students == null || students.size() != 0) throw new java.lang.Exception("readEmpty failed!"); } NUnit.Framework.Test() */ public void readEmpty() throws java.lang.Exception { java.util.ArrayList students; students = StudentsIO.read("empty.txt"); if (students == null || students.size() != 0) throw new java.lang.Exception("readEmpty failed!"); }

9-23 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Assertions Assertions are a common way of denoting failure Idea: –you assert that a particular boolean condition is true –if condition turns out to be true, nothing happens –if condition turns out to be false, an exception is thrown NUnit.Framework.Test() */ public void readEmpty() throws java.lang.Exception { java.util.ArrayList students; students = StudentsIO.read("empty.txt"); System.Diagnostics.Debug.Assert(students != null); System.Diagnostics.Debug.Assert(students.size() == 0); } NUnit.Framework.Test() */ public void readEmpty() throws java.lang.Exception { java.util.ArrayList students; students = StudentsIO.read("empty.txt"); System.Diagnostics.Debug.Assert(students != null); System.Diagnostics.Debug.Assert(students.size() == 0); }

9-24 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Part 4 Other tools & ideas…

9-25 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Other tools & ideas NUnit short demo videos by Martin Schray: WinForms GUI testing? –NUnitForms, Web app testing? –NUnitASP, Other strategies? –programming with invariants, listing pre & post-conditions –these are based on the idea of using assertions in your code: … // at this point in the program, count should be 1, if not through an exception & stop now System.Diagnostics.Debug.Assert(count == 1, "Count==1 failed"); … // at this point in the program, count should be 1, if not through an exception & stop now System.Diagnostics.Debug.Assert(count == 1, "Count==1 failed");

9-26 MicrosoftIntroducing CS using.NETJ# in Visual Studio.NET Summary Unfortunately, errors are a part of being human Errors can be eliminated, but it takes a great deal of effort: –good logic –good design –good programming –good testing You have the tools: –J#, Visual Studio.NET, NUnit, etc.