What is software? Why should it be tested? What is Quality?

What is software? Why should it be tested?

Software is a series of instructions for the computer that perform a particular task, called a program; the two major categories of software are system software and

application software. System software is made up of control programs. Application software is any program that processes data for the user (spreadsheet, word

processor, payroll, etc.).

A software product should only be released after it has gone through a proper process of development, testing and bug fixing. Testing looks at areas such as

performance, stability and error handling by setting up test scenarios under controlled conditions and assessing the results. This is why exactly any software has to be

tested. It is important to note that software is mainly tested to see that it meets the customers’ needs and that it conforms to the standards. It is a usual norm that

software is considered of good quality if it meets the user requirements.

What is Quality? How important is it?

Quality can briefly be defined as “a degree of excellence”. High quality software usually conforms to the user requirements. A customer’s idea of quality may cover a

breadth of features - conformance to specifications, good performance on platform(s)/configurations, completely meets operational requirements (even if not

specified!), compatibility to all the end-user equipment, no negative impact on existing end-user base at introduction time.

Quality software saves good amount of time and money. Because software will have fewer defects, this saves time during testing and maintenance phases. Greater

reliability contributes to an immeasurable increase in customer satisfaction as well as lower maintenance costs. Because maintenance represents a large portion of all

software costs, the overall cost of the project will most likely be lower than similar projects.

Following are two cases that demonstrate the importance of software quality:

Ariane 5 crash June 4, 1996- Maiden flight of the European Ariane 5 launcher crashed about 40 seconds after takeoff
- Loss was about half a billion dollars
- Explosion was the result of a software error
- Uncaught exception due to floating-point error: conversion from a 64-bit integer to a 16-bit signed integer applied to a larger than expected number
- Module was re-used without proper testing from Ariane 4
- Error was not supposed to happen with Ariane 4
- No exception handler

Mars Climate Orbiter - September 23, 1999 - Mars Climate Orbiter, disappeared as it began to orbit Mars.
- Cost about $US 125-million
- Failure due to error in a transfer of information between a team in Colorado and a team in California
- One team used English units (e.g., inches, feet and pounds) while the other used metric units for a key spacecraft operation.