Software Testing
CHAPTER # 9: SLICE-BASED TESTING

Slice Based Testing
Program slicing was introduced by Mark Weiser [WEIS84] where we prepare various subsets
(called slices) of a program with respect to its variables and their selected locations in the
program.
Each variable with one of its location will give us a program slice.
A large program may have many smaller programs (its slices), each constructed for different
variable subsets.
The slices are typically simpler than the original program, thereby simplifying the process of
testing of the program.

Slice Based Testing
“Program slicing is a technique for restricting the behaviour of a program to some specified
subset of interest. A slice S( , n) of program P on variable , or set of variables, at statement n
yields the portions of the program that contributed to the value of just before statement n is
executed. S ( , n) is called a slicing criteria. Slices can be computed automatically on source
programs by analyzing data flow. A program slice has the added advantage of being an executable
program.” [KEIT91]
Slices are smaller than the original program and may be executed independently. Only two things
are important here, variable and its selected location in the program.

Slice Based Testing
Slice: Given a program P and a set V of variables in P, a slice on the variable set V at statement
n, written S(V, n), is the set of all statement fragments in P that contribute to the values of
variables in V at node n.

Backward and Forward Program Slice
Backward Slice: Backward slices refer to statement fragments that contribute to the value of v at
statement n.
Forward Slice: Forward slices refer to all the program statements that are affected by the value of
v and statement n.

Program Slice
Static slice S(v, n) consists of all the statements in a program that determine the value of
variable v at statement n,independent of values used in the statements.
Dynamic slices refer to execution-time execution of portions of a static slice with specific values
of all variables in S(v, n).

Static and Dynamic Slice
1. int z=10;
2. int n;
3. cin>>n;
4. int sum=0;
5. if (n>10)
6. sum = sum + n;
7. else
8. sum = sum – n;
9. cout <<sum;
Static slice for variable
sum
2,3,4,5,6,7,8,9
int n;
cin>>n;
int sum=0;
if (n>10)
sum = sum + n;
else
sum = sum – n;
cout <<sum;
Dynamic slice for
variable sum when n=
15
2,3,4,5,6,9
int n;
cin>>n;
int sum=0;
if (n>10)
sum = sum + n;
cout <<sum;

Program Slicing
Consider the program given below:
1. void main ( )
2. {
3. int a, b, c, d, e;
4. cout<<“Enter the values of a, b and
c”<<endl;
5. cin>>a >>b >>c;
6. d = a+b;
7. e = b+c:
8. cout<<d;
9. cout<<e;
10. }
Slice on criterion S (e, 10) = (1, 2, 3, 4, 5, 7, 9, 10)
1. void main ( )
2. {
3. int a, b, c, d, e;
4. cout<<“Enter the values of a, b and
c”<<endl;
5. cin>>a >>b >>c;
7. e = b+c:
9. cout<<e;
10. }

Program Slicing
Slice on criterion S (e,7) = (1, 2, 3, 4, 5, 7,10)
1. void main ( )
2. {
3. int a, b, c, d, e;
4. cout<<“Enter the values of a, b and
c”<<endl;
5. cin>>a >>b >>c;
7. e = b+c:
10. }
Slice on criterion S (d,10) = (1, 2, 3, 4, 5, 6, 8, 10)
1. void main ( )
2. {
3. int a, b, c, d, e;
4. cout<<“Enter the values of a, b and
c”<<endl;
5. cin>>a >>b >>c;
6. d = a+b;
8. cout<<d;
10. }

Guidelines for Slicing
There are many variables in a program, but their usage may be different in different statements.
The following guidelines may be used for the creation of program slices.
 All statements where variables are defined and redefined should be considered.
 All statements where variables receive values externally should be considered.
 All statements where output of a variable is printed should be considered.
 All statements where some relevant output is printed should be considered.
 The status of all variables may be considered at the last statement of the program.

1. void main()
2. 2. {
3. double a,b,c;
4. double a1,a2,a3;
5. int valid=0;
6.
7. cout<<"Enter first side of the triangle:";
8. cin>>a;
9. cout<<"Enter second side of the triangle:";
10. cin>>b;
11. cout<<"Enter third side of the triangle:";
12. cin>>c;
/*Checks whether a triangle is valid or not*/
13.
if(a>0&&a<=100&&b>0&&b<=100&&c>0&&c<=100)
{
14. if((a+b)>c&&(b+c)>a&&(c+a)>b) {
15. valid=1;
16. }
17. else {
18. valid=-1;
19. }
20. }
21. if(valid==1) {
22. a1=(a*a+b*b)/(c*c);
23. a2=(b*b+c*c)/(a*a);
24. a3=(c*c+a*a)/(b*b);
25. if(a1<1||a2<1||a3<1) {
26. cout<<"Obtuse angled triangle";
27. }
28. else if(a1==1||a2==1||a3==1) {
29. cout<<"Right angled triangle";
30. }
31. else {
32. cout<<"Acute angled triangle";
33. }
34. }
35. else if(valid==-1) {
36. cout<<"nInvalid Triangle";
37. }
38. else {
39. cout<<"nInput Values are Out of Range";
40. }
41.
42. } //end of main

Program Slicing for Triangle problem
All statements where variables are defined and redefined should be considered.
 Variable valid is defined at line 5, and redefined at 15 and 18. we may create S(valid, 5),
S(valid, 15) and S(valid, 18) slices
All statements where variables receive values externally should be considered.
 variables ‘a’, ‘b’ and ‘c’ receive values externally at line 8, 10 and12 respectively. we may create
S(a, 8), S(b, 10) and S(c, 12) slices
All statements where output of a variable is printed should be considered.
All statements where some relevant output is printed should be considered.
 line 26, 29, 32, 36 and 39 are used for printing the classification of the triangle. We may create
S(a1, 26), S(a1, 29), S(a1, 32), S(valid, 36) and S(valid, 39) as slices
The status of all variables may be considered at the last statement of the program.
 line 42 is the last statement of the program. We may create S(a1, 42), S(a2, 42), S(a3, 42),
S(valid, 42), S(a, 42), S(b,42) and S(c, 42) as slices.

Program Slicing for Triangle problem
There are seven variables ‘a’, ‘b’, ‘c’, ‘a1’, ‘a2’, ‘a3’ and ‘valid’ in the program.
We may create many slices as given below:
1. S (a, 8) = {1–8, 42}
2. S (b, 10) = {1–6, 9, 10, 42}
3. S (c, 12) = {1–6, 11, 12, 42}
4. S (a1, 22) = {1–16, 20–22, 34, 42}
5. S (a1, 26) = {1–16, 20–22, 25–27, 34, 41, 42}
6. S (a1, 29) = {1–16, 20–22, 25, 27–31, 33, 34, 41, 42}
7. S (a1, 32) = {1–16, 20–22, 25, 27, 28, 30–34, 41, 42}
8. S (a2, 23) = {1–16, 20, 21,23, 34, 42}
9. S (a2, 26) = {1–16, 20, 21, 23, 25–27, 34, 41, 42}
10.S (a2, 29) = {1–16, 20, 21, 23, 25, 27–31, 33, 34, 41, 42}
11.S (a2, 32) = {1–16, 20, 21, 23, 25, 27, 28, 30–34, 41, 42}

Program Slicing for Triangle problem
12.S (a3, 26) = {1–16, 20, 21, 24–27, 34, 41, 42}
13.S (a3, 29) = {1–16, 20, 21, 24, 25, 27–31, 33, 34, 41,42}
14.S (a3, 32) = {1–16, 20, 21, 24, 25, 27, 28, 30–34, 41, 42}
15.S (valid, 5) = {1–5, 42}
16.S (valid, 15) = {1–16, 20, 42}
17.S (valid, 18) = {1–14, 16–20, 42}
18.S (valid, 36) = {1–14, 16–20, 21, 34–38, 40–42}
19.S (valid, 39) = {1–13, 20, 21, 34, 35, 37–42}

Test Cases
Slice Path a b c Expected Output
1 S(a, 8)/S(a,42) 1-8, 42 20 No Output
2 S(b, 10)/S(b,42) 1-6, 9, 10, 42 20 No Output
3 S(c, 12)/S(c,42) 1-6, 11, 12, 42 20 No Output
4 S(a1, 22) 1–16, 20–22, 34, 42 30 20 40 No output
5 S(a1, 26) 1–16, 20–22, 25–27, 34, 41, 42 30 20 40 Obtuse angled triangle
6 S(a1, 29) 1–16, 20–22, 25, 27–31, 33, 34, 41, 42 30 40 50 Right angled triangle
7 S(a1, 32) 1–16, 20–22, 25, 27, 28, 30–34, 41, 42 50 60 40 Acute angled triangle
8 S(a1, 42) 1–16, 20–22, 34, 42 30 20 40 No output
9 S(a2, 23) 1–16, 20, 21, 23, 34, 42 30 20 40 No output
10 S(a2, 26) 1–16, 20, 21, 23, 25–27, 34, 41, 42 40 30 20 Obtuse angled triangle
11 S(a2, 29) 1–16, 20, 21, 23, 25, 27–31, 33, 34, 41, 42 50 40 30 Right angled triangle

Test Cases
Slice Path a b c Expected Output
12 S(a2, 32) 1–16, 20, 21, 23, 25, 27, 28, 30–34, 41, 42 40 50 60 Acute angled triangle
13 S(a2, 42) 1–16, 20, 21, 23, 34, 42 30 20 40 No output
14 S(a3, 24) 1–16, 20, 21, 24, 34, 42 30 20 40 No output
15 S(a3, 26) 1–16, 20, 21, 24–27, 34, 41, 42 20 40 30 Obtuse angled triangle
16 S(a3, 29) 1–16, 20, 21, 24, 25, 27–31, 33, 34, 41, 42 40 50 30 Right angled triangle
17 S(a3, 32) 1–16, 20, 21, 24, 25, 27, 28, 30–34, 41, 42 50 40 60 Acute angled triangle
18 S(a3, 42) 1–16, 20, 21, 24, 34, 42 30 20 40 No output
19 S(valid,5) 1–2, 5, 42 No output
20 S(valid,15) 1–16, 20, 42 20 40 30 No output
21 S(valid,18) 1–14, 16–20, 42 30 10 15 No output
22 S(valid,36) 1–14, 16–20, 21, 34–38, 40–42 30 10 15 Invalid triangle

Test Cases
Slice Path a b c Expected Output
23 S(valid,39) 1–13, 20, 21, 34, 35, 37–42 102 -1 6 Input values out of range
24 S(valid,42) 1–14, 16–20, 42 30 10 15 No output

References
Software Testing: A Craftsman’s Approach, by Paul C. Jorgensen & Byron DeVries 5th Edition
Software Testing, by Yogesh Singh