Black Box Testing-Defination,tools used,methods

Black Box Testing

Black Box Testing, also known as Behavioural Testing, is a software testing method in which the internal structure/design/implementation of the item being tested is not known to the tester. Just giving the input and checking for correct output. These tests can be functional or non-functional, though usually functional.

This method is named so because the software program, in the eyes of the tester, is like a black box; inside which one cannot see.

This method of attempts to find errors in the following categories:

• Incorrect or missing functions
• Interface errors
• Errors in data structures or external database access
• Behavior or performance errors
• Initialization and termination errors

Tools used for Black Box testing:
Black box testing tools are mainly record and playback tools. These tools are used for regression testing that to check whether new build has created any bug in previous working application functionality. These record and playback tools records test cases in the form of some scripts like TSL, VB script, Java script, Perl.

Advantages	Disadvantages
Well suited and efficient for large code segments. Code Access not required. Clearly separates user's perspective from the developer's perspective through visibly defined roles. Large numbers of moderately skilled testers can test the application with no knowledge of implementation, programming language or operating systems.	Limited Coverage since only a selected number of test scenarios are actually performed. Inefficient testing, due to the fact that the tester only has limited knowledge about an application. Blind Coverage, since the tester cannot target specific code segments or error prone areas. The test cases are difficult to design.

Methods of Black box Testing:

1. Equivalence Partitioning:
Equivalence partitioning is a black box testing method that divides the input domain of a program into classes of data from which test cases can be derived.

How is this partitioning performed while testing:
1. If an input condition specifies a range, one valid and one two invalid classes are defined.
2. If an input condition requires a specific value, one valid and two invalid equivalence classes are defined.
3. If an input condition specifies a member of a set, one valid and one invalid equivalence class is defined.
4. If an input condition is Boolean, one valid and one invalid class is defined.

2. Boundary Value Analysis:
Many systems have tendency to fail on boundary. So testing boundary values of application is important. Boundary Value Analysis (BVA) is a test Functional Testing technique where the extreme boundary values are chosen. Boundary values include maximum, minimum, just inside/outside boundaries, typical values, and error values.

Extends equivalence partitioning
Test both sides of each boundary
Look at output boundaries for test cases too
Test min, min-1, max, max+1, typical values

BVA techniques:
1. Number of variables
For n variables: BVA yields 4n + 1 test cases.
2. Kinds of ranges
Generalizing ranges depends on the nature or type of variables
Advantages of Boundary Value Analysis
1. Robustness Testing – Boundary Value Analysis plus values that go beyond the limits
2. Min – 1, Min, Min +1, Nom, Max -1, Max, Max +1
3. Forces attention to exception handling

Limitations of Boundary Value Analysis
Boundary value testing is efficient only for variables of fixed values i.e boundary.

Error Guessing

Error Guessing is a software testing technique that generates test cases which can find the error by using past experience of tester. The key concept is using the prior software testing experience to supplement other software testing techniques. 

The known error in any software is varied so using input from experienced tester for that software is a good idea. From my software testing experience, the typical errors are related to "divide by zero" and "various date and time format".