Topic: Test Case Design Techniques

The test case design techniques are broadly grouped into two categories: Black box techniques, White box techniques and other techniques that do not fall under either category.

Black Box (Functional)
- Specification derived tests
- Equivalence partitioning
- Boundary Value Analysis
- State-Transition Testing
White Box (Structural)
- Branch Testing
- Condition Testing
- Data Definition - Use Testing
- Internal boundary value testing
Other- Error guessing

Specification Derived Tests
As the name suggests, test cases are designed by walking through the relevant specifications. It is a positive test case design technique.

Equivalence Partitioning
Equivalence partitioning is the process of taking all of the possible test values and placing them into classes (partitions or groups). Test cases should be designed to test one value from each class. Thereby, it uses fewest test cases to cover the maximum input requirements.

For example, if a program accepts integer values only from 1 to 10. The possible test cases for such a program would be the range of all integers. In such a program, all integers upto to 0 and above 10 will cause an error. So, it is reasonable to assume that if 11 will fail, all values above it will fail and vice versa.

If an input condition is a range of values, let one valid equivalence class be the range (0 or 10 in this example). Let the values below and above the range be two respective invalid equivalence values (i.e. -1 and 11). Therefore, the above three partition values can be used as test cases for the above example.

Boundary Value Analysis
This is a selection technique where the test data are chosen to lie along the boundaries of the input domain or the output range. This technique is often called as stress testing and incorporates a degree of negative testing in the test design by anticipating that errors will occur at or around the partition boundaries.

For example, a field is required to accept amounts of money between $0 and $10. As a tester, you need to check if it means upto and including $10 and $9.99 and if $10 is acceptable. So, the boundary values are $0, $0.01, $9.99 and $10.

Now, the following tests can be executed. A negative value should be rejected, 0 should be accepted (this is on the boundary), $0.01 and $9.99 should be accepted, null and $10 should be rejected. In this way, it uses the same concept of partitions as equivalence partitioning.

State Transition Testing
As the name suggests, test cases are designed to test the transition between the states by creating the events that cause the transition.

Branch Testing
In branch testing, test cases are designed to exercise control flow branches or decision points in a unit. This is usually aimed at achieving a target level of Decision Coverage. Branch Coverage, need to test both branches of IF and ELSE. All branches and compound conditions (e.g. loops and array handling) within the branch should be exercised at least once.

Condition Testing
The object of condition testing is to design test cases to show that the individual components of logical conditions and combinations of the individual components are correct. Test cases are designed to test the individual elements of logical expressions, both within branch conditions and within other expressions in a unit.

Data Definition – Use Testing
Data definition-use testing designs test cases to test pairs of data definitions and uses. Data definition is anywhere that the value of a data item is set. Data use is anywhere that a data item is read or used. The objective is to create test cases that will drive execution through paths between specific definitions and uses.

Internal Boundary Value Testing
In many cases, partitions and their boundaries can be identified from a functional specification for a unit, as described under equivalence partitioning and boundary value analysis above. However, a unit may also have internal boundary values that can only be identified from a structural specification.

Error Guessing
It is a test case design technique where the testers use their experience to guess the possible errors that might occur and design test cases accordingly to uncover them.

Using any or a combination of the above described test case design techniques; you can develop effective test cases.