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This module provides an introduction to software testing. Topics covered include basic definitions of testing, validation and verification; the levels of testing from unit testing through to acceptance testing; the relationship with requirements and design specifications; and test documentation.

Introduction

Software Testing is the process of executing a program or system with the intent of finding errors. Or, it involves any activity aimed at evaluating an attribute or capability of a program or system and determining that it meets its required results. Software is not unlike other physical processes where inputs are received and outputs are produced. Where software differs is in the manner in which it fails. Most physical systems fail in a fixed (and reasonably small) set of ways. By contrast, software can fail in many bizarre ways. Detecting all of the different failure modes for software is generally infeasible.

Unlike most physical systems, most of the defects in software are design errors, not manufacturing defects. Software does not suffer from corrosion, wear-and-tear, generally it will not change until upgrades, or until obsolescence. So once the software is shipped, the design defects, or bugs, will be buried in and remain latent until activation.

Software bugs will almost always exist in any software module with moderate size: not because programmers are careless or irresponsible, but because the complexity of software is generally intractable, and humans have only limited ability to manage complexity. It is also true that for any complex systems, design defects can never be completely ruled out.

Discovering the design defects in software, is equally difficult, for the same reason of complexity. Because software and any digital systems are not continuous, testing boundary values are not sufficient to guarantee correctness. All the possible values need to be tested and verified, but complete testing is infeasible. Exhaustively testing a simple program to add only two integer inputs of 32-bits (yielding 2^64 distinct test cases) would take hundreds of years, even if tests were performed at a rate of thousands per second. Obviously, for a realistic software module, the complexity can be far beyond the example mentioned here. If inputs from the real world are involved, the problem will get worse, because timing and unpredictable environmental effects and human interactions are all possible input parameters under consideration.

A further complication has to do with the dynamic nature of programs. If a failure occurs during preliminary testing and the code is changed, the software may now work for a test case that it didn't work for previously. But its behavior on pre-error test cases that it passed before can no longer be guaranteed. To account for this possibility, testing should be restarted. The expense of doing this is often prohibitive.

An interesting analogy parallels the difficulty in software testing with the pesticide (known as the Pesticide Paradox): Every method you use to prevent or find bugs leaves a residue of subtler bugs against which those methods are ineffectual. But this alone will not guarantee to make the software better, because the Complexity Barrier principle states: Software complexity (and therefore that of bugs) grows to the limits of our ability to manage that complexity. By eliminating the (previous) easy bugs you allowed another escalation of features and complexity, but his time you have subtler bugs to face, just to retain the reliability you had before. Society seems to be unwilling to limit complexity because we all want that extra bell, whistle, and feature interaction. Thus, our users always push us to the complexity barrier and how close we can approach that barrier is largely determined by the strength of the techniques we can wield against ever more complex and subtle bugs.

Questions & Answers

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khan Reply
what is coding
YUSUF Reply
hello, I don't know anything about software but I have this passion to learn. where do I start from pls
Oliver Reply
computer science class or just take a introduction to computers class. You can always try to find a mentor or self teach yourself as well.
Dustin
what important of software
Tom Reply
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Yogesh
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Mark
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Mark
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Tom
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Khizer
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Khizer
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Tom
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Khizer
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Shey
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Tom
I want to know more about programming
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Xotambek
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Peterson
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Xotambek
l would like to know what do I need if I want to.create a sun glasses where you can see everything when you're sharing something via bluetooth
Peterson
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Peterson
I have so many things that I want to create in the technology industry
Peterson
but I need a group of people who are willing bring ideas on the table and work together to make success
Peterson
wow
Shey
What sorts of feild knowledge do you need?
leo
Mr. Peteson pinchinat, hello!
leo
I don't really know what do I need to learn that's why I'm asking
Peterson
I need help to create all those things that I want to.
Peterson
peterson pinchinat I have so many ideas and much more things in my mind
Khizer
hello
Purity
even Me guys
Mark
if you have many ideas than I have so let's work together let's build a team . let's put our ideas and start working together to make success.
Peterson
I really like to work with software
Khizer
any I like that people how have interest on new technology and software developer, engineering
Khizer
wow!!! we have something in common.
Peterson
great then we can share some ideas and then see how we can make things happen
Peterson
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Khizer
we have to find a way. I'm living in Brooklyn what about you?
Peterson
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Khizer
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Khizer
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Peterson
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Khizer
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Khizer
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Shey
Yes ,It is possible to be a programmer without University Degree.You have a lot professional courses that you access and register for on the net.Please get hook and search ..thanks
NICCK-PAT
Great ,I am NICCk-PAT in Paris France.
NICCK-PAT
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Dustin
how do i create software
Ahmad Reply
Hii
Sameer
what is the IEEE ?
Shankar Reply
a external device cable capable of transferring large amounts of data at high speed.
Dustin
really
Shey
How to learn in this app? ..help me
HANAN Reply
how make a software engineer
Ajaykumar Reply
how to use this app ..help me
HANAN
what is incremental model?
Shir Reply
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preethi Reply
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preethi
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Mounika Reply
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Mounika
Tell me medam what is the project do you have
Harinathreddy
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Mounika
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Harinathreddy
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Sameer
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Amanson
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Yogesh
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Ahmad
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Shey
am new in the field
Shey
differentiate between writing and jotting
Mmem Reply
configration management
Ravi Reply
what is a computer software
Chinaza Reply
Computer software is programming code executed on a computer processor at either the machine-level or the level of the operating system. ... The physical components of a computer are the hardware, and the digital programs running on the hardware are the software.
SATYAM
9292
Saeed
what is sofftware
Mohammed Reply
Software, in its most general sense, is a set of instructions or programs instructing a computer to do specific tasks. Software is a generic term used to describe computer programs. Scripts, applications, programs and a set of instructions are all terms often used to describe software.
SATYAM
now I got it
Ali
if I get your point, software is basically a set of instructions or programs run on hardware to perform a specific task.
Samuel

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Source:  OpenStax, Software engineering. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10790/1.1
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