Software Testing and Quality Assurance

1. Software Testing and Quality Assurance Lecture 7 - Software Testing Techniques

2. Lecture Outline • Discuss Equivalence Partitioning • How to select test cases based on equivalence Partitioning. • Discuss Boundary-value Analysis • How to select test cases based on boundary-value analysis.

3. Equivalence Partitioning • Partition the input of a program using the functional requirements. • Test inputs are executed on the program, and • The tester evaluates whether the output of the program is in the expected output domain.

4. Choosing Equivalence Classes • Aim is to minimize the number of test cases required to cover all of the Equivalence Classes (EC). • Identify the initial EC. • Identify overlapping EC, and • Eliminate them by making the overlapping part a new equivalence classes. • Select one element from each EC as the first test input; and • Work out the expected result for that test input.

5. Identify initial equivalence classes • No clear formula • We need to build up some judgment and intuition. • Guidelines to identify potential EC. • We may need to choose extra cases in order to explore difficult subsets of the input domain.

6. Identify initial equivalence classes - Guidelines • Input condition specifies range of vales, • Identify one valid EC • Two invalid EC • One for the set of values below the range • One for the set of values above the range. • For example, range of values 1…. 99, • The valid EC 1…99; and • Two invalid EC i.e. {x | x < 1} and {x | x > 99}

7. Identify initial equivalence classes - Guidelines • Input condition specifies a set of input values. • A valid EC for each element of the set, and • One EC class for the elements not in the set. • For example, input selected from a set of N inputs, we need N + 1 EC; • One valid EC for each element of set,and • One invalid EC for element outside the set.

8. Identify initial equivalence classes - Guidelines • Input condition specifies a ‘must be’ situation, • Identify one valid EC and one invalid EC. • For example, if character input must be numeric, we need two EC • A valid EC --- { s | the first character of s is a numeric} • One invalid EC --- {s | the first character of s is not a numeric}

9. Identify initial equivalence classes - Guidelines • If program handles each valid input differently, then • define one valid EC per valid input. • For example, input from a menu • Define one valid EC for each menu item. • If elements in EC are handled differently by the program, then • Split the EC into smaller EC Some of the guidelines are very general in nature. Domain knowledge and experience plays a key role in identifying EC.

10. Eliminating Overlapping EC Overlapping EC EC 2 EC 1

11. Eliminating Overlapping EC - Example Disjoint EC • A - an empty list • B - list with one element • C - list with at least two element • D - a sorted list; and • E - an unsorted list Two or more elements are either sorted or unsorted. • Unsorted list with at least 2 elements. • Sorted list with at least 2 elements.

12. Selecting Test Cases • Once EC have been identified • Any value from EC is identified to be as likely to produce a failure as any other value in that class. • Thus, any element of the class servers as a test input. • However, selecting just any value in EC may not be optimal for finding faults. • For example, faulty implementation of square function.

13. Important Question? • How to resolve the overlap so that we do not derive too many test cases?

14. Boundary-value Analysis (BVA) • Greater number of errors occur at the boundaries of the input domain. • Select test cases to explore the boundary conditions of a program. • BVA complements equivalence partitioning. • Rather then selecting any element from EC, • BVA leads to the selection of test cases at the ‘edges’ of the class.

15. Boundary-value Analysis • Faults are more likely to introduced at boundary because • Unsure of the correct boundary for an input condition; • Have incorrectly tested the boundary.

16. Example - Triangle Program • A program reads floating point values from the standard input. • The three values are interpreted as representing the lengths of the sides of a triangle. • Program prints a message that states whether the triangle is • Equilateral, isosceles, scalene or invalid.

17. Example - Triangle Program • Equilateral triangle • Only one boundary where x = y = z. • Test cases to explore this boundary • (3,3,3) On Point • (2.99, 3, 3) Off Point Below • (3.001,3,3) Off Point Above

18. Example - Triangle Program • Isosceles Triangle • x = y AND y ≠z, y = z AND z ≠x ….. • Test cases to explore the boundary x = y AND y ≠z • (3,3,4) On Point • (2.99, 3, 4) Off Point Below • (3.001,3,4) Off Point Above

19. Boundary-value Analysis - Guidelines • Input condition specifies a range bounded by values a and b, • test cases should designed with values a and b as well as just above and just below a and b. • Input condition specifies a number of values, • Test cases should check the minimum and maximum numbers.

20. Boundary-value Analysis - Guidelines • Guidelines 1 and 2 are applied to output domain as well. • A program generates temperature vs pressure table. • Test case should create output that produces maximum (and minimum) allowable number of table entries.

21. Boundary-value Analysis and Equivalence Partitioning • One or more test cases be selected from the edge of the EC or close to the EC. • Simply requires that any element in the equivalence class will do. • Test cases be derived from the output conditions. • Only the input domain is usually considered.

22. Key points • Equivalence partitioning is one of the oldest and still most widely used method for selecting test cases based on a partitioning of the input domain. • Boundary conditions are predicates that apply directly on, above, and beneath the input boundaries of input and output EC.