Principles of Software Engineering by Utpal Roy, Jadavpur University, Kolkata, India

1. Software Testing Technique
White Box and Black Box Testing Technique
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2. Software Testing Technique
Testing Objective
1. Testing is a process of executing program ( test program ) with an
intention of finding errors ( bugs ).
2. A good test case is one that has a high probability of finding an as-
yet-undiscovered error.
3. A successful test is the one that has uncovered an as-yet-
undiscovered error.
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3. Software Testing Technique
Testing Principles
1. All tests should be traceable to customer requirements.
2. Test planning and test preparation should be planned long before
testing begins.
3. Test case should be designed keeping the ‘Pareto’ principle in mind
which states that, 80% of all the errors uncovered during the testing
process are located within the 20% of the program components.
4. Exhaustive testing is never possible because of resource ( man-
power, time, money etc. ) constraints.
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4. Software Testing Technique
Testability – what it is ?
How easily a computer program can be tested.
How adequately a particular set of tests will cover the product.
How easily the product can be checked and repaired in the field.
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5. Software Testing Technique
Test Case Design
 Test case should be designed keeping two test situations in mind.
They are :-
1. White Box Testing
2. Black Box Testing
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6. Software Testing Technique
White Box Testing
This method of testing assumes, the tester has a good knowledge
about the source code which is under consideration for testing.
Depending upon the structure of the source code, the test cases are
designed.
Each of the test case is supposed to test a unique path through the
code. This method of testing is also called Basis Path Testing.
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7. Software Testing Technique
White Box Testing (contd.)
 Let’s take an example program of which we need to design test cases for
white box testing.
int find_max ( int a, int b, int c )
{
int max;
if ( a>b ) then max=a;
else max=b;
if ( max<c ) then max=c;
return max;
}
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8. Software Testing Technique
White Box Testing (contd.)
Flow Chart of the Previous Program
1 Declare a,b,c;Define max
T
2 a>b Max = a 3
F
4 Max = b
T
5 max<c Max=c 6
F
7 Return max
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9. Software Testing Technique
White Box Testing (contd.)
Cyclomatic Complexity
Before we proceed to write the test cases we have to know how many
test cases will be there at the most.
This can be known by a software metric called ‘Cylomatic Complexity’.
The Cyclomatic Complexity provides the quantitative measure of
the logical complexity of a program.
With regard to white box testing, cyclomatic complexity gives us the
upper bound for the number of tests that must be conducted to ensure
that all statements have been executed at least once.
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10. Software Testing Technique
White Box Testing (contd.)
Cyclomatic Complexity
The Cyclomatic Complexity can be computed by adding one to the
total number of decision box in the program.
As for the program mentioned before, there are 2 decision box shown
in the flow chart. So, the cyclomatic complexity is 2+1=3.
So, at the most there are three independent path in the program. To
find out those independent path, we have to convert the flow chart to
flow graph.
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11. Software Testing Technique
White Box Testing (contd.)
Rules for Flow Chart to Flow Graph Conversion
All the process box and the decision diamond should be numbered in
the flow chart.
A decision diamond should map to a node.
A single process box or a sequence of process box should map to a
single node.
A process box and a decision box can be mapped together to a single
node also.
The flow should map to a link or edge between the nodes.
An edge must terminate to a node, even if the node does not represent
any procedural statement.
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12. Software Testing Technique
White Box Testing (contd.)
1,2
An independent path is a path, where
At least one edge has not been traversed
4 Before. With this rule, we get 3 independent
3
Path. They are :-
1. 1,2  3  5  7
2. 1,2  4  5  7
5
3. 1,2  3  5  6  7
Since, the cyclomatic complexity for this
6 Flow graph is 3; there cannot be more than
3 independent path.
7
Flow Graph
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13. Software Testing Technique
White Box Testing (contd.)
Test Cases for the previous program
Test Case 1 [ for the path 1 ]
Input : a>b; a>c
Expected Output : a
Test Case 2 [ for the path 2 ]
Input : b>a; b>c
Expected Output : b
Test Case 3 [ for the path 3 ]
Input : c>a; c>b
Expected Output : c
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14. Software Testing Technique
Black Box Testing
It is also known as behavioral testing
It focuses on the functional requirement of the software.
It is complementary rather then alternative to white box testing.
Black Box Testing is performed during the later stages of the software
testing; unlike white box testing which is performed during the early
stages of software testing.
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15. Software Testing Technique
Black Box Testing (contd.)
The reason for doing black box testing
1. It uncovers incorrect or missing functions.
2. It detects interface errors.
3. It can detect internal data structure errors or external data base
errors.
4. It can point out whether performance of the software is below
the desired level.
5. It can spot initialization or termination error.
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16. Software Testing Technique
 Black Box Testing (contd.)
Test Case Design for Black Box Testing
1. Design test cases in such a way, so that it covers all
the functional requirements of the software.
2. Design test cases to test the performance criteria of
the software.
3. Design test cases to test the most frequently used
inputs given by the user.
4. Design test cases to test the sensitive inputs given by
the user.
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17. Software Testing Technique
 Black Box Testing (contd.)
Test Case Design for Black Box Testing (contd.)
5. Design test cases to test the boundary condition of the
software.
6. Design test cases to test the behavior of the software
for reasonable amount of negative inputs.
7. Design test cases to test the maximum load and stress
capability of the software.
8. Design test cases to test the security aspects of the
software.
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18. Software Testing Technique
 Loop Testing
Testing Technique :-
1. Skip the loop entirely.
2. Only one pass through the loop.
3. Two passes through the loop.
4. If n is the maximum no of allowable
passes through the loop, then m
passes ( m<n ) through the loop.
5. n-1, n, n+1 passes through the loop.
Simple Loop
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19. Software Testing Technique
 Loop Testing ( contd. )
Testing Technique :-
1. Start at innermost loop. Set all outer loops
to minimum values.
2. Conduct simple loop tests for innermost
loop.
3. Work outward, conducting tests for the next
loop, but keeping all other outer loops at
minimum values and other nested loops to
typical values.
4. Continue until all loops have been tested.
Nested Loop
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20. Software Testing Technique
 Home Task
A. Design test cases for white box testing for the
following set of Programs mentioned below.
1. An array contains n number of integers. Find the
maximum number from that array.
2. A program reads 3 integer values. The 3 values
represents the 3 sides of a triangle. The program prints
a message telling whether the triangle is scalene,
isosceles, or equilateral.
B. Design test cases for black box testing for the program
shown in the beginning of this class.
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