Black box testing one of the most common word that has been used by almost all the testers. In this article we will understand the meaning of black box testing and we will discuss about how black box testing is performed in real world.
It is one of the most common testing methods perform by most of the tester. This method does not need lot of knowledge about the coding part of the product. If a tester has understand the requirement specification properly, then he/she can easily test the application. In this method we mostly verify and validate the customer requirement through the developed software. Tester only knows about the input parameter and output parameter that are used to verify. Tester try to cover all the valid and invalid inputs while performing a black box testing.
In the initial phase of testing its good to be a black box tester, but for a long term it’s hard to survive with this. Because it’s very hard to discover all kind of issue with black box testing only. So to survive in this fast running IT world, everyone have to be updated related to different kind of testing.

Types of Black Box Testing Techniques: Following black box testing techniques are used for testing the software application.

• Boundary Value Analysis (BVA)
• Equivalence Class Partitioning
• Decision Table based testing
• Cause-Effect Graphing Technique
• Error Guessing

1) Boundary Value Analysis (BVA):

Boundary Value Analysis is the most commonly used test case design method for black box testing. As all we know the most of errors occurs at boundary of the input values. This is one of the techniques used to find the error in the boundaries of input values rather than the centre of the input value range.

Boundary Value Analysis is the next step of the Equivalence class in which all test cases are design at the boundary of the Equivalence class.

Let us take an example to explain this:

Suppose we have software application which accepts the input value text box ranging from 1 to 1000, in this case we have invalid and valid inputs: Below are the combination of test case for input box by using Boundary Value Analysis.

This is testing techniques is not applicable only if input value range is not fixed i.e. the boundary of input is not fixed.

2) Equivalence Class Partitioning

The equivalence class partition is the black box test case design technique used for writing test cases. This approach is use to reduce huge set of possible inputs to small but equally effective inputs. This is done by dividing inputs into the classes and gets one value from each class. Such method is used when exhaustive testing is most wanted & to avoid the redundancy of inputs.
In the equivalence partitioning input are divided based on the input values:

• If input value is Range, then we one valid equivalence class & two invalid equivalence classes.
• If input value is specific set, then we one valid equivalence class & one invalid equivalence classes.
• If input value is number, then we one valid equivalence class & two invalid equivalence classes.
• If input value is Boolean, then we one valid equivalence class & one invalid equivalence classes.
3) Cause and Effect Graphing technique

Cause-Effect Graph graphically shows the connection between a given outcome and all issues that manipulate the outcome. Cause Effect Graph is a black box testing technique. It is also known as Ishikawa diagram because of the way it looks, invented by Kaoru Ishikawa or fish bone diagram.

It is generally uses for hardware testing but now adapted to software testing, usually tests external behaviour of a system. It is a testing technique that aids in choosing test cases that logically relate Causes (inputs) to Effects (outputs) to produce test cases.

A “Cause” stands for a separate input condition that fetches about an internal change in the system. An “Effect” represents an output condition, a system transformation or a state resulting from a combination of causes.

Cause Effect diagram can be used under these Circumstances:

• To determine the current problem so that right decision can be taken very fast.
• To narrate the connections of the system with the factors affecting a particular process or effect.
• To recognize the probable root causes, the cause for a exact effect, problem, or outcome.

Benefits of making cause-Effect Diagram

• It finds out the areas where data is collected for additional study.
• It motivates team contribution and uses the team data of the process.
• Uses synchronize and easy to read format to diagram cause-and-effect relationships.
• Point out probable reasons of difference in a process.
• It enhances facts of the procedure by helping everyone to learn more about the factors at work and how they relate.
• It assists us to decide the root reasons of a problem or quality using a structured approach.