🔰Techniques Used in Black Box Testing

Boundary Value Analysis

• Decision boundaries are places where the behaviour of the system changes

• It is an important technique as it is widely recognised that values on the boundaries cause more errors in the system

• Therefore, the tester should always check the boundaries as if the system fails. It is likely to fail on the decision boundaries

• It can be verified using boundary values, upper boundary values, lower boundary values

Here is an example:

Equivalence Class Portioning

• Usually it is not possible to perform exhaustive testing when there is large test data either due to lack of time or budgets constraints

• It is very efficient technique used to cut down the number of test data to test the application

• If the given data range is very larger, it can be portioned into equal halves and the boundary value analysis can be applied to write the testcase

Here is an example:

• According to our example, the test data can be portioned into following classes,

• Now to test the application, tester uses one value from each partition

• tests the application with only three numbers (any one from each partition)

• Each number of class partitions generates the same result. Therefore, the technique is called Equivalence class partitioning

Decision Table

Combined inputs with logical conditions are the Test cases in the decision table. The four areas of the Decision table are the condition stub, condition entries (TC1, TC2 etc), the action stub and the entry. The table’s column is the rule specifying the condition under which the action named in the action stub takes place.

State Transition Technique

The changes in the input conditions change the state of the application under test. This technique allows to test the behaviour of an application. With help of this technique, we can enter various input conditions in sequence. This testing requires both positive as well as negative values to test the system behaviour.

• This technique should be used only to test the application for a limited set of input conditions

• Also, to test under a sequence of events which happens in the application

Example:

1.If a user enters a valid password in any of the first three attempts, the user will be able to login successfully.

2.If a user enters the invalid password in the first or second attempt, the user will be prompted to re-enter the password.

When the user enters the password incorrectly in third attempt, an action is taken, and the user will get blocked.

If the user gives the correct PIN number, he or she can access the granted state.

Following table is created based on the diagram above:

When the user enters the correct PIN, the state is transitioned to Access granted. If the user enters an Incorrect PIN, then moved to next state. If he or she does the same thing in third attempt account gets blocked.

Error Guessing

It is a software testing technique based on guessing the error which can prevail in the code. Error guessing is an Experience-based technique where the test analyst uses his or her prior experience to guess the defects in the application.

This approach identifies the list of possible errors first and then the analyst writes the test cases to expose those errors. To design test cases based on this technique, the testers can use the prior experience to identify the conditions.