unit-v -software quality. to develop and deliver robust system, we need a high level of confidence...

Unit-V -SOFTWARE QUALITY

To develop and deliver robust system, we need a high level of confidence thatEach component will behave correctlyCollective behavior is correctNo incorrect collective behavior will be

produced Debugging and testing Quality assurance test, testing

strategies, OO on Software quality, test plan and test cases.

Reason why quality assurance is needed,Computers are infamous for doing what we

tell them to do, not necessarily what we want them to do.

To close this gap, code must be free of errors or bugs that cause unexpected results

Software debugging system can provide tools for finding errors in programs and correcting them

Different kinds of errors areSyntax errorsRun-Time errorsLogic errors

Quality assurance testing can be divided into two major categoriesError based testing (testing the boundary

condition)Scenario based testing (Usage-based

testing) Error based Testing

Search a given class’s method for particular clues of interests, then describe how these clues should be tested

Scenario based TestingConcentrates on what the user

does, not what the product does

Extend of testing a system is controlled by many factors, such as the risks involved, limitations on resources and deadlines

There are many test strategies, but most testing uses a combination of themBlack box testingWhite box testingTop-Down testingBottom-Up testing

Black Box Testing Used to represent a system whose

inside workings are not available for inspection.

Test items are tested as “Black”, since its logic is unknown, all that is known is what goes in and what comes out, i.e. input and output

Works nicely in testing objects in OO environment

Black Box Testing

Input Output

White Box TestingAssumes that the specific logic is important

and must be tested to guarantee the system’s proper functioning.

Main use is in error-based testing, when we already have tested all objects of an application and all external or public methods of an object that are of greater importance

One form of white box testing, called path testing, makes certain that each path in a object’s method is executed at least once during testing.

Two types of path testing areStatement based testingBranch based testing

Top-Down Testing It assumes that the main logic or

object interactions and systems message of the application need more testing than an individual object’s method or supporting logic

It can detect the design flows early in the implementation

It supports testing the user interface and event-driven systems

Top-Down Testing It can test the navigation through screens

and verify that it matches the requirement, users can see, at an early stage, how the final application will look and feel.

Useful for Scenario-based testing.Useful to test subsystem and system

integration.

Bottom-Up testing Starts with the details of the system

and proceeds to higher levels by a progressive aggregation of details until they collectively for the requirements for the system.

This approach is more appropriate for testing the individual object in a system.

Test each object, combine them and test their interaction and the message passed among object by utilizing the top-down approach.

Bottom-Up testing In bottom-up, start with methods and

classes that call or rely on no others, then progress to next level up. Those methods and classes that use only the bottom level ones already tested

It leads to integration testing which leads to system testing

To have a comprehensive testing scheme, the test must cover all methods or a good majority of them.

All services of the system should be checked atleast once.

To test a system, given input and received output checked with expected output

The main objectives of testing are: Testing is the process of executing a

program with the intent of finding errors. A good test case is the one that has a

high probability of detecting an as-yet undiscovered error.

A test case is a set of what-if questions Thomas has developed guidelines that

have been adapted for the UA Describe which feature or service your test

attempts to cover If the test case is based on a use-case, it is

good idea to refer to the use-case name. Use-cases are the source of test cases.

Specify what you are testing and which particular feature

Test the normal use of the object’s methods.

Test the abnormal but reasonable use of object’s method.

Test the boundary conditionTest object’s interactions and message sent

among themThe internal quality of the software, such as

reusability and extendibility should be assessed as well.

Test plan is developed to detect and identify potential problems before delivering the software to its users

It provides the roadmap for testing activities, whether usability, user satisfaction or quality assurance tests.

Steps needed to create a test plan:Objectives of the testDevelopment of a test caseTest analysis

All passed tests should be reported with the revised program called regression testing, which can discover errors introduced during the debugging process

For a small application, the designer or the design team usually will develop the test plan and test cases and in some situations, actually will perform the tests.

Many organizations have a separate team, such as a quality assurance group, that works closely with the design team and is responsible for these activities

Most software companies also use beta testing a popular inexpensive and effective way to test software on a select group of the actual users of the system

In contrast, alpha testing is done by in-house testers, such as programmers, software engineering and internal users.

You may have requirements that dictate a specific appearance or format for your test plan.

Test plan should contain a schedule and a list of required resources

After you have determined what types of testing are necessary, you need to document specifically what you are going to do

A configuration control system provides a way of tracking the changes to the code.

A well thought out design tends to produce better code and result in more complete testing, so it is a good idea to buy to keep the plan up to date.

At the end of each month, take time to complete routine updates.

Software is tested to determine whether it conforms to the specifications of requirements.

Software is maintained when errors are found and corrected and software is extended when new functionality is added to an already existing program.

There are different reasons for testing such as to test for potential problems in a proposed design or to compare two or more designs to determine which is better, given a specific task or set of tasks

Testing the whole system and detecting bugs is more difficult than testing smaller pieces of the application as it is being developed.

Testing must take place on a continuous basis and this refining cycle must continue through out the development process until we are satisfied with the results.

The steps to successful testing:Understand and communicate the

business case for improved testingDevelop an internal infrastructure to

support continuous testing.Look for leaders who will commit to and

own the processMeasures and document your findings in a

defect recording systemPublicize improvements as they are made

and let people know what they are doing better

Bug Locating Principle: Think If you reach an impasse, sleep on it. If the impasse remains, describe the

problem to someone else Use debugging tools Experimentation should be done as a

last

Debugging Principle: Where there is a one bug, there is likely

to be another Fix the error, not just the symptom of it The probability of the solution being

correct drops as the size of the program increases

Because of the possibility that an error correction will create a new error

Review Questions What is testing ? List out the different testing strategies. What is black box testing? When would you use white box testing? If you don’t know what is inside the box, how would you test it? What is the importance of developing a test case? What is white box testing? What is path testing? What is statement testing coverage? What is branch testing coverage? What is regression testing? What is a test plan? What steps are followed in developing a test plan? What is top-down testing? What is bottom -up testing? What are guidelines for developing test plans? What do you mean by continuous testing? What are the Myer’s debugging principles? What is debugging? What is error based testing? Give an example. What is scenario -based testing? What are two types of path testing? Differentiate beta testing and alpha testing? What are the steps involved in successful testing? Define Unit Testing?

Bibiliography Object oriented system development by

Ali Brahami Object oriented methodology by Booch A text book on UML by Srimathi