Page 43 - SOFTWARE TESTING & QUALITY ASSURANCE

Software Testing and Quality Assurance

can be easily depicted using state diagrams. These state diagrams consist of states and transitions. Every
program has two important states, the start state which indicates the beginning of the program and the
end state which indicates the end of the program. In between these two states, a number of intermediate
states represent the logical flow of the software. During the executions, the program flows from one
state to another. This change of state is called state transition.

The Windows paint program expresses itself in different states. When the
application is opened, the cursor takes the pencil tool as the default state. When
a different tool is selected, say an air-brush, the cursor changes its state to bring
out the properties of the air-brush. The internal working of the software toggles
every time the user selects a different tool. This change can be termed as state
transition.

All software that is event driven makes use of state based techniques to analyze the
program flow. For example, the GUI programs make use of state based techniques both
at the design stage and at the testing stage.

The state diagram is a graph that depicts all the states and transitions taking place during the flow. The
tester checks the states and transitions occurring at each level of the state diagram. The tester has to
check each state and the transition that takes place, since every state is unique and each transition is a
new operation that is performed on the current state to generate an output that is moving to the next
state. This helps the tester to understand the flow of the software and detect the occurrence of the bugs
based on states and transition.
Let us consider a program where a transition has to happen from state A to B
and from B to C. The tester checks if the transition happens from state A to C
and from C to B. This incorrect transition will be considered as a bug in the
software.
State based technique helps to obtain a model that depicts the behavior of a program very clearly.
However, drawing a state diagram is a challenging task. Any software has many states and a transition
associated with it. Depicting the same can be a complex process.
3.2.5 Random Testing and Mutation Testing

Many other techniques of software testing are being used by testers around the world to obtain efficient
testing results. Two of the most popular and widely used testing techniques are random testing and
mutation testing.

Random Testing
In random testing, the tester provides random inputs to the test software and checks the output of the
software against the expected output. Any mismatch in the actual output and expected output will be
treated as a bug.
In a mathematical expression,
C = 2 * B;
The variable B can take values from -500 to 500. The test can be carried out for
five random values- 24, -348, 75, 499, and -1. The expected result would be 48, -
696, 150, 998, and -2 respectively. The expected result is compared with the
actual result when this expression is executed.
Random testing is one of the popular testing techniques which is also called as Gorilla testing or Adhoc
testing. This is discussed in detail in Chapter 9.

Mutation Testing
In this type of testing, the tester makes minor modifications in the program’s source code and performs
the test. If the program clears the test even after it is modified, the program is considered to be
defective. Any such modification is called mutation. The main objective of mutation testing is to check

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