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Analysis and Design
Fundamentals of Software Testing
Testing is basically a process to detect errors in the software product. Before
going into the details of testing techniques one should know what errors are.
In day-to-day life we say whenever something goes wrong there is an error. This
definition is quite vast. When we apply this concept to software products then
we say whenever there is difference between what is expected out of software and
what is being achieved, there is an error.
For the output of the system, if it differs from what was required, it is due
to an error. This output can be some numeric or alphabetic value, some formatted
report, or some specific behavior from the system. In case of an error there may
be change in the format of out, some unexpected behavior from system, or some
value different from the expected is obtained. These errors can due to wrong analysis,
wrong design, or some fault on developer's part.
All these errors need to be discovered before the system is implemented at
the customer's site. Because having a system that does not perform as desired
be of no use. All the effort put in to build it goes waste. So testing is done.
And it is equally important and crucial as any other stage of system development.
For different types of errors there are different types of testing techniques.
In the section that follows we'll try to understand those techniques.
Objectives of testing
First of all the objective of the testing should be clear. We can define testing
as a process of executing a program with the aim of finding errors. To perform
testing, test cases are designed. A test case is a particular made up artificial
situation upon which a program is exposed so as to find errors. So a good test
case is one that finds undiscovered errors. If testing is done properly, it uncovers
errors and after fixing those errors we have software that is being developed
according to specifications.
Test Information Flow
Testing is a complete process. For testing we need two types of inputs. First
is software configuration. It includes software requirement specification, design
specifications and source code of program. Second is test configuration. It is
basically test plan and procedure.
Software configuration is required so that the testers know what is to be expected
and tested whereas test configuration is testing plan that is, the way how the
testing will be conducted on the system. It specifies the test cases and their
expected value. It also specifies if any tools for testing are to be used. Test
cases are required to know what specific situations need to be tested. When tests
are evaluated, test results are compared with actual results and if there is some
error, then debugging is done to correct the error. Testing is a way to know about
quality and reliability. Error rate that is the occurrence of errors is evaluated.
This data can be used to predict the occurrence of errors in future.
Fig 9.1 Testing Process
Test Case design
We now know, test cases are integral part of testing. So we need to know more
about test cases and how these test cases are designed. The most desired or obvious
expectation from a test case is that it should be able to find most errors with
the least amount of time and effort.
A software product can be tested in two ways. In the first approach only the
overall functioning of the product is tested. Inputs are given and outputs are
checked. This approach is called black box testing. It does not care about the
internal functioning of the product.
The other approach is called white box testing. Here the internal functioning
of the product is tested. Each procedure is tested for its accuracy. It is more
intensive than black box testing. But for the overall product both these techniques
are crucial. There should be sufficient number of tests in both categories to
test the overall product.
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