1. ECE 453 – CS 447 – SE 465 Software Testing & Quality Assurance Lecture 6 Instructor Paulo Alencar

2. Overview Functional Testing Boundary Value Testing (BVT)
Boundary Value Analysis
Robustness Testing
(Robust) Worst Case Testing
Special Value Testing
Equivalence Class Testing
Weak Equivalence Class Testing
Strong Equivalence Class Testing
Traditional Equivalence Class testing
Decision Table Based testing

3. Equivalence Class Testing
The use of equivalence class testing has two motivations:
Sense of complete testing
Avoid redundancy
Equivalence classes form a partition of a set that is a collection of mutually disjoint subsets whose union is the entire set.
Two important implications for testing:
The fact that the entire set is represented provides a form of completeness
The disjointness assures a form of non-redundancy

4. Equivalence Classes
The idea of equivalence class testing is to identify test cases by using one element from each equivalence class.
If the equivalence classes are chosen wisely this greatly reduces the potential redundancy among test cases.
The key point in equivalence class testing is the choice of the equivalence relation that determines the classes (partitions).
We will differentiate below, between weak and strong equivalence class testing.

5. Equivalence Class Selection
It tends to be a “craft”:
no dependence on knowledge of code, only the specification
needs knowledge of input domain that usually goes beyond what an interface design specification provides
familiarity with specifications
must understand how inputs are mutually dependent.

6. Example
Let us consider a program P with 3 inputs: a, b and c and the corresponding input domains are A, B, and C.
define the partition:
A = A1 U A2 U A3
B = B1 U B2 U B3 U B4
C = C1 U C2

7. define a1, a2 and a3 as:
let ai be a “representative” or “typical” value within its respective equivalence class (e.g. the midpoint in a linear equivalence class).
similarly define bi and ci.
test cases can be stated for the inputs <a,b,c> in terms of the representative points.
the basic idea behind the techniques is that one point within an equivalence class is just as good as any other point within the same class.

8. Weak Equivalence Class Testing
Weak equivalence class testing is accomplished by using one variable from each equivalence class in a test case.
The minimum number of test cases is equal to the number of classes in the partition with the largest number of subsets.
From the previous example, we have:
Test Case
Variable a
Variable b
Variable c
WE1 a1 b1 c1
WE2 a2 b2 c2
WE3 a3 b3
WE4 b4

9. Strong Equivalence Class Testing
Strong equivalence class testing is based on the Cartesian Product of the partition subsets.
From the previous example, this would generate:
3 * 4 * 2 = 24 test cases
Generates more test cases which test for any interaction between the representative values from each of the subsets.
For either method, it may be possible to define equivalence relations for the program output, then test cases can also be based on these.

10. Test Case # a b c SE1 a1 b1 c1 SE2 c2 SE3 b2 SE4 SE5 b3 SE6 SE7 b4 SE8

11. Traditional View
The traditional view of equivalence class testing defines equivalence in terms of validity that is, test cases determined from the valid and invalid values for each input variable.
For each input variable there are valid and invalid values.
In the traditional approach, these are identified and numbered, and then incorporated into test cases in the weak sense as presented above.

12. Traditional View
Given valid and invalid sets of inputs, the traditional equivalence testing strategy identifies test cases as follows:
For valid inputs, use one value from each valid class (as in what we have called weak equivalence class testing). In this context, each input in these test cases will be valid.
For invalid inputs, a test case will have one invalid value and the remaining values will be valid. In this context, a “single failure” should cause the test case to fail.
If the input variables have defined ranges, then the test cases from traditional equivalence class testing will always be a subset of those that would be generated by robustness testing.

13. Issues with Traditional View
There are two problems with the traditional equivalence testing:
The first is that, very often, the specification does not define what the expected value for an invalid test case should be.
The second problem is that strongly typed languages eliminate the need for the consideration of invalid inputs.

14. Example
For example consider a program with two input variables size and weight:
valid ranges:
S1: 0 < size < 200
W1: 0 < weight < 1500
corresponding invalid ranges might be:

15. Test Cases Example (Traditional View)
size
weight
Expected Output
TE1
100
750
whatever it should be
TE2 -1
invalid input
TE3
1500
TE4
TE5
200

16. Equivalence Test Cases for the Triangle Problem (Output Domain)
In the problem statement we note that there are four possible outputs:
Not a Triangle
Isosceles
Equilateral
Scalene
We can use these to identify output (range) equivalence classes:
R1= {<a, b, c> | the triangle with sides a, b, c, is equilateral}
R2= {<a, b, c> | the triangle with sides a, b, c, is isosceles}
R3= {< a, b, c> | the triangle with sides a, b, c, is scalene}
R4= {a, b, c> | sides a, b, c do not form a triangle}
These classes yield the following simple set of test cases:

17. Sample Test Cases based on Output Domain
Expected
Output
OE1 5
Equilateral
OE2 2 3
Isosceles
OE3 4
Scalene
OE4 1
Not a Triangle

18. Equivalence Test Cases for the Triangle Problem (Input Domain)
If we base the equivalence classes on the input domain, we will obtain a larger set of test cases. We can define the sets:
D1= {<a,b,c> | a=b=c}
D2= {<a,b,c> | a=b, a≠c}
D3= {<a,b,c> | a=c, a≠b}
D4= {<a,b,c> | b=c, a≠b}
D5= {<a,b,c> | a≠b, a≠c, b≠c}
As a separate property we can apply the triangle property to see even if the input constitutes a triangle
D6= {<a, b, c> | a ≥ b+c}
D7= {<a, b, c> | b ≥ a+c}
D8= {<a, b, c> | c ≥ a+b}
If we wanted also we could split D6 into
D6’={<a, b, c> | a = b+c} and
D6’’= {<a, b, c> | a > b+c}

19. Equivalence Test Cases for the NextDate Problem (Input Domain)
Nextdate is a function of three variables, month, day, and year and these have ranges defined as:
1 ≤ month ≤ 12
1 ≤ day ≤ 31
1812 ≤ year ≤ 2012
We will examine below the valid, invalid equivalence classes, strong, and weak equivalence class testing.

20. Traditional Test Cases
The valid equivalence classes are:
M1= {month | 1 ≤ month ≤ 12}
D1= {day | 1 ≤ day ≤ 31}
Y1= {year | 1812 ≤ year ≤ 2012}
The invalid equivalence classes are:
M2= {month | month < 1}
M3= {month | month > 12}
D2= {day | day < 1}
D3= {day | day > 31}
Y2= {year | year < 1812}
Y3= {year | year > 2012}
These classes yield the following test cases, where the valid inputs are mechanically selected from the approximate middle of the valid range:

21. Traditional Test Cases
Case ID
Month
Day
Year
Expected
Output
TE1 6 15
1912
6/16/1912
TE2 -1
Invalid
TE3 13
TE4
TE5 32
TE6
1811
TE7
2013

22. Choice of Equivalence Classes
If we more carefully chose the equivalence relation, the resulting equivalence classes will be more useful
M1= {month | month has 30 days}
M2= {month | month has 31 days}
M3= {month | month is February}
D1= {day | 1 ≤ day ≤ 28}
D2= {day | day = 29}
D3= {day | day = 30}
D4= {day | day=31}
Y1= {year | year = 1900}
Y2= {year | 1812 ≤ year ≤ 2012 AND year ≠ 1900 AND (0 = year mod 4}
Y3= {year | 1812 ≤ year ≤ 2012 AND 0 ≠ year mod 4}

23. Weak Equivalence Class Test Cases
Case ID
Month
Day
Year
Expected Output
WE1 6 14
1900
6/15/1900
WE2 7 29
1912
7/30/1912
WE3 2 30
1913
Invalid
WE4 31

24. Strong Equivalence Test Cases
CASE ID
Month
Day
Year
Output
SE1 6 14
1900
6/15/1900
SE2
1912
6/15/1912
SE3
1913
6/15/1913
SE4 29
6/30/1900
SE5
6/30/1912
SE6
6/30/1913
SE7 30
7/1/1900
SE8
7/1/1912
SE9
7/1/1913
SE10 31
ERROR
SE11
SE12
SE13 7
7/15/1900
SE14
7/15/1912
SE15
7/15/1913
SE16
7/30/1900
SE17
7/30/1912
SE18
7/30/1913

25. Strong Equivalence Test Classes
CASE ID
Month
Day
Year
Output
SE19 7 30
1900
7/31/1900
SE20
1912
7/31/1912
SE21
1913
7/31/1913
SE22 31
8/1/1900
SE23
8/1/1912
SE24
8/1/1913
SE25 2 14
2/15/1900
SE26
2/15/1912
SE27
2/15/1913
SE28 29
ERROR
SE29
3/1/1912
SE30
SE31
SE132
SE33
SE34
SE35
SE36

26. Guidelines and Considerations
The traditional form of equivalence testing is generally not as thorough as weak equivalence testing, and in its turn, not as thorough as strong equivalence testing
If error conditions is a priority we can extend strong equivalence testing to include invalid classes
Equivalence class testing is appropriate when input data is defined in terms of ranges and sets of discrete values.
Logic of functionality of the program can help define the equivalence classes
Strong equivalence takes the presumption that variables are independent, otherwise it generates some “error” test cases
Can be strengthened by using it with domain testing (boundary value):
Reuse the work to define the ranges
Does not consider elements at equivalence class boundaries
Need to expand ECT to include BVT-like requirements (domain testing)