Testing an Object Oriented Application

What Testing an Object Oriented Application covers

Testing an Object Oriented Application is examined in Unit AS 1, Introduction to Object Oriented Development — a written examination. It covers why an object oriented application must be tested, choosing test data: normal, boundary and erroneous, writing a test plan for a class, testing a class method by method, testing constructors and object state, testing inheritance and overridden methods, testing error handling paths, dry runs and trace tables, test harnesses, drivers and stubs, recording and interpreting test results and evaluating a test plan and re-testing.

The 11 subtopics

Each one has its own page. CCEA AS Software Systems Development students sit this topic in the first year.

• Why an object oriented application must be testedPurpose of testing a program, unit testing and regression testing.Open →
• Choosing test data: normal, boundary and erroneousTest data, equivalence partition and testing with an empty value.Open →
• Writing a test plan for a classWhat each entry states, choosing data for every method and every path, testing the constructor and the state it leaves, and writing the expected result before anything is run.Open →
• Testing a class method by methodExercising one method at a time with the object in a known state, checking what it returns and what it changes, and testing methods that depend on the order they are called in.Open →
• Testing constructors and object stateObject's state and tested about an attribute the constructor never assigns.Open →
• Testing inheritance and overridden methodsConfirming an inherited method still behaves in the subclass, that an overridden method is the one that actually runs, and that a call through a base-class reference reaches the right version.Open →
• Testing error handling pathsForcing each failure the code claims to handle, checking the exception is caught rather than escaping, that the message is useful, and that the object is left in a usable state afterwards.Open →
• Dry runs and trace tablesDry run and trace table.Open →
• Test harnesses, drivers and stubsTest harness, test driver and assertion in a test.Open →
• Recording and interpreting test resultsRecorded as the actual result of a test, pass actually and first thing to check when a test fails.Open →
• Evaluating a test plan and re-testingJudging whether a plan covered every method, path and boundary, what a plan that found nothing suggests, re-running after a fix, and re-running the tests around it.Open →

What you need to know

Answer each one before you reveal it.

Take Testing an Object Oriented Application further

The same content, four other ways.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is the purpose of testing a program?

   Model answer

   Testing runs the program with chosen data to expose any difference between what it actually does and what it was agreed it should do, so faults are found before users meet them.

2. 2

   Why can testing never prove that a program is free of faults?

   Model answer

   Testing shows only that the cases tried behaved correctly, and the number of possible inputs is far too large to try them all, so testing demonstrates that faults are present rather than that none remain.

3. 3

   Why does a fault inside a class matter more than a fault in a one-off block of code?

   Model answer

   A class is written to be used many times and in many places, so a single fault inside it is repeated in every object created from it and in every program that reuses the class.

4. 4

   Why is a class a natural unit to test on its own?

   Model answer

   A class gathers its data and the methods that act on it in one place behind a defined set of public methods, so the class can be exercised by calling those methods and examining what comes back.

5. 5

   What does unit testing mean when the unit is a class?

   Model answer

   Unit testing a class means creating objects from it and calling its methods with chosen values, then checking the returned results and the object's state, with the rest of the application absent.

6. 6

   Which basic tests must every class in an object oriented application pass?

   Model answer

   Object oriented applications are first given the basic tests every class must survive: each constructor leaves the object in the intended state, each method returns the right value for ordinary data, and each validation rule refuses the values it is meant to refuse.

What is inside Levo

Six ways to work the same material.

Testing an Object Oriented Application revision questions

Is Testing an Object Oriented Application examined at AS in CCEA Software Systems Development?

Yes. It sits in AS Unit 1, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.

What does Testing an Object Oriented Application cover in CCEA AS-Level Software Systems Development?

11 subtopics: why an object oriented application must be tested, choosing test data: normal, boundary and erroneous, writing a test plan for a class, testing a class method by method, testing constructors and object state, testing inheritance and overridden methods, testing error handling paths, dry runs and trace tables, test harnesses, drivers and stubs, recording and interpreting test results and evaluating a test plan and re-testing. Each one has its own page with questions and model answers.

How is Testing an Object Oriented Application organised?

By the CCEA CL4 specification, subtopic by subtopic, so it matches the order you are taught it in.