There are different methods
that can be used for software testing. This chapter briefly describes the
methods available.
The technique of testing
without having any knowledge of the interior workings of the application is
called black-box testing. The tester is oblivious to the system architecture
and does not have access to the source code. Typically, while performing a black-box
test, a tester will interact with the system's user interface by providing
inputs and examining outputs without knowing how and where the inputs are
worked upon.
The following table lists the
advantages and disadvantages of black-box testing.
|
Advantages |
Disadvantages |
|
● Well suited and efficient for large code segments. ● Code access is not required. ● Clearly separates user's perspective from the developer's perspective through visibly defined roles. ● Large numbers of
moderately skilled testers can test the application with no knowledge of
implementation, programming language, or operating systems. |
● Limited coverage, since only a selected number of test scenarios is actually performed. ● Inefficient testing, due to the fact that the tester only has limited knowledge about an application. ● Blind coverage, since the tester cannot target specific code segments or error-prone areas. ● The test cases are
difficult to design. |
White-box testing is the
detailed investigation of internal logic and structure of the code. White-box
testing is also called glass testingor open-box testing.
In order to perform white-box testing on an application, a
tester needs to know the internal workings of the code.
The tester needs to have a
look inside the source code and find out which unit/chunk of the code is
behaving inappropriately.
The following table lists the
advantages and disadvantages of white-box testing.
|
Advantages |
Disadvantages |
|
● As the tester has knowledge of the source code, it becomes very easy to find out which type of data can help in testing the application effectively. ● It helps in optimizing the code. ● Extra lines of code can be removed which can bring in hidden defects. ● Due to the tester's
knowledge about the code, maximum coverage is attained during test scenario
writing. |
● Due to the fact that a skilled tester is needed to perform white-box testing, the costs are increased. ● Sometimes it is impossible to look into every nook and corner to find out hidden errors that may create problems, as many paths will go untested. ● It is difficult to
maintain white-box testing, as it requires specialized tools like code analyzersand debugging tools. |
Grey-box testing is a
technique to test the application with having a limited knowledge of the
internal workings of an application. In software testing, the phrase the more
you know, the better carries a lot of weight while testing an application.
Mastering the domain of a
system always gives the tester an edge over someone with limited domain
knowledge. Unlike black-box testing, where the tester only tests the
application's user interface; in grey-box testing, the tester has access to
design documents and the database. Having this knowledge, a tester can prepare
better test data and test scenarios while making a test plan.
|
Advantages |
Disadvantages |
|
● Offers combined benefits of black-box and white-box testing wherever possible. ● Grey box testers don't rely on the source code; instead they rely on interface definition and functional specifications. ● Based on the limited information available, a grey-box tester can design excellent test scenarios especially around communication protocols and data type handling. ● The test is done from the
point of view of the user and not the designer. |
● Since the access to source code is not available, the ability to go over the code and test coverage is limited. ● The tests can be redundant if the software designer has already run a test case. ● Testing every possible
input stream is unrealistic because it would take an unreasonable amount of
time; therefore, many program paths will go untested. |
The following table lists the
points that differentiate black-box testing, grey-box testing, and white-box
testing.
|
Black-Box Testing |
Grey-Box Testing |
White-Box Testing |
|
The internal workings of
an application need not be known. |
The tester has limited
knowledge of the internal workings of the application. |
Tester has full knowledge
of the internal workings of the application. |
|
Also known as closed-box
testing, data-driven testing, or functional testing. |
Also known as translucent
testing, as the tester has limited knowledge of the insides of the application. |
Also known as clear-box
testing, structural testing, or code-based testing. |
|
Performed by end-users
and also by testers and developers. |
Performed by end-users
and also by testers and developers. |
Normally done by testers
and developers. |
|
Testing is based on
external expectations - Internal behavior of
the application is unknown. |
Testing is done on the
basis of high-level database diagrams and data flow diagrams. |
Internal workings are
fully known and the tester can design test data accordingly. |
|
It is exhaustive and the
least time-consuming. |
Partly time-consuming and
exhaustive. |
The most exhaustive and
time-consuming type of testing. |
|
Not suited for algorithm
testing. |
Not suited for algorithm
testing. |
Suited for algorithm
testing. |
|
This can only be done by
trial-and-error method. |
Data domains and internal
boundaries can be tested, if known. |
Data domains and internal
boundaries can be better tested. |