Page 40 - SOFTWARE TESTING & QUALITY ASSURANCE

Unit 3: Black Box Testing

The test cases have to be defined effectively in order to find the bugs. The entire test process will
depend on the test cases.
A software application undergoes a dynamic black box test. The test case
defines that the application has to produce an output D when the inputs A and
B are given. If the application gives an output C, then the application fails the
test case and this is a bug.
There are various techniques used to perform dynamic black box testing. Some of the important
techniques are test-to-pass and test-to-fail, equivalence partitioning, data testing and state testing. We
will be discussing them in detail in subsequent sections.
3.2.1 Test to Pass and Test to Fail
The test-to-pass approach checks for the standard functions of the program. However, the test cases
focus mainly to check the normal operation of the software. The test cases do not push the software to
its limit or will not try to break the software. They try to find out the bugs by operating the software
under normal conditions.
The test-to-fail approach test cases push the software to its extreme. The main focus is to push the
software to its limit and check for bugs when the software is operated under extreme conditions. The
tester tries to provide extreme and erroneous values as inputs to check how the software can be broken.

A calculator application is developed to calculate the average of more than 1000
integer values. The calculator first has to be set to "Find average" mode and all
the values whose average has to be found will be entered. Once all the values
have been entered the “equal” button can be clicked to display the average of all
the entered numbers. As a tester when you perform test-to-pass, you calculate
the average for few hundred values, but will not cross the thousand values
mark. This is testing the application by providing the normal input.
When you perform test-to-fail, you provide more than thousand values and
check the output of the software. You even take it further by providing more
than two thousand values and check the output produced by the application.
Such inputs might overload the application. This helps the tester to check the
maximum number of values for which the application can find the average.

It is important to note that while performing the test, the tester should first begin the test with test-to-
pass, and check whether the software works fine without any bugs. Once it clears test-to-pass, the tester
can perform test-to-fail.
3.2.2 Equivalence Partitioning
Equivalence partitioning, also called as equivalence classing, is a process of classifying the test cases and
grouping them into different categories or classes. This method helps to reduce the number of test cases
to a finite number of test cases without compromising on the quality of the test being carried out.
The main objective of partitioning is to identify the test cases that perform same kind of testing and
generate similar output. Since the test cases within one class are considered to be equivalent, picking up
one test case from each class would be sufficient to detect the bugs in the software. This technique helps
to reduce the volume of test cases considerably.

The class can be divided into two types, valid class and invalid class. All the classes which fall under
valid type are values that satisfy the condition. Classes that do not satisfy the condition fall under the
invalid class.

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