Testing a class

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Chapter 8

• Testing a class

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This chapter discusses

• Testing in general.
• Testing a single class.
• Test plans.
• Building a test system.

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Testing

• Testing is an activity whose goal is to determine
  if the implementation is correct.
• A successful test is one that reveals some
  previously undiscovered error.

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Testing Phases

• Test activities are determined and test data
  selected.
• The test is conducted and test results are
  compared with expected results.

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Test design

• Begins with an analysis of
• The functional specifications of the system.
• The ways in which the system will be used
  (referred to as use cases).
• Testing based on these considerations is referred
  to as black box testing.

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Black Box testing

• The test designer ignores the internal structure
  of the implementation in developing the test.
• The expected external behavior of the system
  drives the selection of test activities and data.
• The system is treated as a black box whose
  behavior can be observed, but whose internal
  structure cannot.

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Test case

• Test cases are defined by
• A statement of case objectives.
• The data set for the case.
• The expected results.

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Equivalency groups

• Test cases are chosen from each equivalency
  group.
• Particular attention is paid to data that lie on
  group boundaries.

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Test plan

• A test plan is a document that describes the test
  cases giving the purpose of each case, the data
  values to be used, and the expected results.
• Test design should be carried out concurrently
  with system development.
• Developing and refining test cases based on the
  implementation of the system is referred to as
  white box testing.
• A test plan can be based on class specifications
  only.

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Test system

• Test systems allow us to interact with the object
  we want to test.
• The test system will let us create the object to
  be tested and then act as a client of the object.

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Testing Counter

• Class specifications
• public class Counter
• A simple integer counter.
• public Counter ()
• Create a new Counter initialized to 0.
• public int count ()
• The current count.
• ensure
• this.count() gt 0
• public void reset ()
• Reset this Counter to 0.
• public void increment ()
• Increment the count by 1.
• public void decrement ()
• Decrement the count by 1. If the count is 0, it
  is not decremented.

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Possible system

• Enter number denoting action to perform
• Increment..............1
• Decrement..............2
• Reset..................3
• Create a new Counter...4
• Exit...................5
• Enter choice.
• 1
• The current count is 1
• Enter number denoting action to perform
• Increment..............1
• Decrement..............2
• Reset..................3
• Create a new Counter...4
• Exit...................5
• Enter choice.
• 1
• The current count is 2 ...

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Building a test system

• The test system will be composed of two objects
• A Counter to be tested.
• A test driver to invoke the Counters methods.
• The test driver prompts the user with a menu,
  gets input from the user, and provides output in
  the form of the count.

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CounterTUI

• TUI -gt Textual User Interface.

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Basic input/output

• Basic I/O consists of reading from standard input
  (keyboard) and writing to standard output
  (monitor).

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Basic input/output (cont.)

• We will use methods provided by the authors
  (OOJ.basicIO.BasicFileWriter, OOJ.basicIO.BasicFil
  eReader).
• public BasicFileWriter ()
• Create a BasicFileWriter attached to standard
  output.
• public void displayLine (String line)
• Write the specified line to standard output.
• public BasicFileReader ()
• Create a BasicFileReader attached to standard
  input.
• public void readInt()
• Reads a new int from standard input.
• public int lastInt()
• Returns the int read by readInt().
• public void readline ()
• Read rest of line from standard input.

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CounterTUI specifications

• public class CounterTUI
• A text-based test driver for the class Counter.
• public CounterTUI ()
• Create a new test driver with a Counter to test.
• public void start ()
• Conduct the test.

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CounterTUI implementation

• public class CounterTUI
• public CounterTUI ()
• input new
• OOJ.basicIO.BasicFileReader()
• output new OOJ.basicIO.BasicFileWr
  iter()
• counter new Counter()
• private OOJ.basicIO.BasicFileReader
• input
• private OOJ.basicIO.BasicFileWriter
• output
• private Counter counter

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CounterTUI implementation (cont.)

• If we look at what happens when the test is
  conducted, we see that the following sequence of
  actions are repeated over and over
• Display menu to the user and prompt the user for
  input.
• Get the users input.
• Perform requested action.
• Display results.

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CounterTUI implementation (cont.)

• We define an instance variable to hold the users
  choice.
• private int choice // the users most //
  recent choice
• The local methods we will create are specified as
  follows.
• private void displayMenuPrompt ()
• Display the menu to the user.
• private void getChoice ()
• Get the users choice.
• private void executeChoice ()
• Perform the action indicated by this.choice, and
  display the results
• to the user.

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While loop

• A while loop continues to perform an action as
  long as a condition is true.
• The while statement is composed of a condition (a
  boolean expression) and another statement, the
  body.
• syntax
• while ( condition )
• body

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Implementation

• main method the top-level method that initiates
  execution of a system.
• Although the main method is defined in a class,
  it is really outside the object-oriented
  paradigm.
• Its only purpose should be to create the top
  level objects and get the system started.

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Implementation (cont.)

• /
• A test system for the class Counter.
• /
• public class CounterTest
• /
• Create the user interface, start
• the system.
• /
• public static void main (String argv)
• CounterTUI theInterface new
• CounterTUI()
• theInterface.start()

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Test plan

• action expected comment
• increment 1 increment from initial
  state
• increment 2 sequence of increments
• increment 3
• increment 4
• decrement 3 sequence of
  decrements
• decrement 2
• increment 3 increment follows
  decrement
• reset 0
• increment 1 increment follows reset
• decrement 0
• decrement 0 decrement 0 count
• reset 0
• decrement 0 decrement follows reset
• create 0 initial state
• decrement 0 decrement from initial
  state

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Weve covered

• The process of testing.
• Test systems.
• Text-based user interface.
• read-process-write loop.
• while loops.
• main method.

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Glossary