Software Testing Profesional.
I have covered what is White box Testing
in previous article. Here I will concentrate on Black box testing. BBT
advantages, disadvantages and and How Black box testing is performed i.e
the black box testing techniques.
Black box testing treats the system as a “black-box”,
so it doesn’t explicitly use Knowledge of the internal structure or
code. Or in other words the Test engineer need not know the internal
working of the “Black box” or application.
Main focus in black box testing is on functionality of the system as a whole. The term ‘behavioral testing’ is also used for black box testing and white box testing is also sometimes called ‘structural testing’.
Behavioral test design is slightly different from black-box test design
because the use of internal knowledge isn’t strictly forbidden, but
it’s still discouraged.
Each testing method has its own advantages
and disadvantages. There are some bugs that cannot be found using only
black box or only white box. Majority of the applicationa are tested by
black box testing method. We need to cover majority of test cases so
that most of the bugs will get discovered by blackbox testing.
Black
box testing occurs throughout the software development and Testing life
cycle i.e in Unit, Integration, System, Acceptance and regression
testing stages.
Tools used for Black Box testing:
Black box testing tools are mainly record and playback tools. These
tools are used for regression testing that to check whether new build
has created any bug in previous working application functionality. These
record and playback tools records test cases in the form of some
scripts like TSL, VB script, Java script, Perl.
Advantages of Black Box Testing
- Tester can be non-technical.
- Used to verify contradictions in actual system and the specifications.
- Test cases can be designed as soon as the functional specifications are complete
Disadvantages of Black Box Testing
- The test inputs needs to be from large sample space.
- It is difficult to identify all possible inputs in limited testing time. So writing test cases is slow and difficult
- Chances of having unidentified paths during this testing
Methods of Black box Testing:
Graph Based Testing Methods:
Each and every application is build up of some objects. All such
objects are identified and graph is prepared. From this object graph
each object relationship is identified and test cases written
accordingly to discover the errors.
Error Guessing:
This is purely based on previous experience and judgment of tester.
Error Guessing is the art of guessing where errors can be hidden. For
this technique there are no specific tools, writing the test cases that
cover all the application paths.
Boundary Value Analysis:
Many systems have tendency to fail on boundary. So testing boundry
values of application is important. Boundary Value Analysis (BVA) is a
test Functional Testing technique where the extreme boundary values are
chosen. Boundary values include maximum, minimum, just inside/outside
boundaries, typical values, and error values.
Extends equivalence partitioning
Test both sides of each boundary
Look at output boundaries for test cases too
Test min, min-1, max, max+1, typical values
BVA techniques:
1. Number of variables
For n variables: BVA yields 4n + 1 test cases.
2. Kinds of ranges
Generalizing ranges depends on the nature or type of variables
Advantages of Boundary Value Analysis
1. Robustness Testing – Boundary Value Analysis plus values that go beyond the limits
2. Min – 1, Min, Min +1, Nom, Max -1, Max, Max +1
3. Forces attention to exception handling
Limitations of Boundary Value Analysis
Boundary value testing is efficient only for variables of fixed values i.e boundary.
Equivalence Partitioning:
Equivalence partitioning is a black box testing method that divides the
input domain of a program into classes of data from which test cases
can be derived.
How is this partitioning performed while testing:
1. If an input condition specifies a range, one valid and one two invalid classes are defined.
2. If an input condition requires a specific value, one valid and two invalid equivalence classes are defined.
3. If an input condition specifies a member of a set, one valid and one invalid equivalence class is defined.
4. If an input condition is Boolean, one valid and one invalid class is defined.
Comparison Testing:
Different independent versions of same software are used to compare to each other for testing in this method.
Reference- http://www.softrel.org/stgb.html
http://www.softwaretestinghelp.com/black-box-testing/
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