BLACK BOX TESTING

Subject: BLACK BOX TESTING Sat Oct 16, 2010 8:24 am

BLACKBOX TESTING
Introduction

Black box testing takes an external perspective of the test object to derive test cases. These tests can be functional or non-functional, though usually functional. The test designer selects valid and invalid input and determines the correct output. There is no knowledge of the test object's internal structure.
This method of test design is applicable to all levels of software testing: unit, integration, functional testing, system and acceptance. The higher the level, and hence the bigger and more complex the box, the more one is forced to use black box testing to simplify. While this method can uncover unimplemented parts of the specification, one cannot be sure that all existent paths are tested.

Contents:
 Testing Strategies/Techniques
 Black Box Testing Strategy
 Black Box Testing Example
 Advantages and Disadvantages
 Dimensions for Examining Testing

Testing Strategies/Techniques
• black box testing should make use of randomly generated inputs (only a test range should be specified by the tester), to eliminate any guess work by the tester as to the methods of the function
• data outside of the specified input range should be tested to check the robustness of the program
• boundary cases should be tested (top and bottom of specified range) to make sure the highest and lowest allowable inputs produce proper output
• the number zero should be tested when numerical data is to be input
• stress testing should be performed (try to overload the program with inputs to see where it reaches its maximum capacity), especially with real time systems
• crash testing should be performed to see what it takes to bring the system down
• test monitoring tools should be used whenever possible to track which tests have already been performed and the outputs of these tests to avoid repetition and to aid in the software maintenance
• other functional testing techniques include: transaction testing, syntax testing, domain testing, logic testing, and state testing.
• finite state machine models can be used as a guide to design functional tests
• According to Beizer the following is a general order by which tests should be designed:
1. Clean tests against requirements.
2. Additional structural tests for branch coverage, as needed.
3. Additional tests for data-flow coverage as needed.
4. Domain tests not covered by the above.
5. Special techniques as appropriate--syntax, loop, state, etc.
6. Any dirty tests not covered by the above

Black Box Testing Strategy
Black Box Testing is not a type of testing; it instead is a testing strategy, which does not need any knowledge of internal design or code etc. As the name "black box" suggests, no knowledge of internal logic or code structure is required. The types of testing under this strategy are totally based/focused on the testing for requirements and functionality of the work product/software application. Black box testing is sometimes also called as "Opaque Testing", "Functional/Behavioral Testing" and "Closed Box Testing".
The base of the Black box testing strategy lies in the selection of appropriate data as per functionality and testing it against the functional specifications in order to check for normal and abnormal behavior of the system. Now a days, it is becoming common to route the Testing work to a third party as the developer of the system knows too much of the internal logic and coding of the system, which makes it unfit to test the application by the developer.

In order to implement Black Box Testing Strategy, the tester is needed to be thorough with the requirement specifications of the system and as a user, should know, how the system should behave in response to the particular action.

Various testing types that fall under the Black Box Testing strategy are: functional testing, stress testing, recovery testing, volume testing, User Acceptance Testing (also known as UAT), system testing, Sanity or Smoke testing, load testing, Usability testing, Exploratory testing, ad-hoc testing, alpha testing, beta testing etc.

These testing types are again divided in two groups: a) Testing in which user plays a role of tester and b) User is not required.

Black Box Testing Strategy
Testing method where user is not required:
Functional Testing:
In this type of testing, the software is tested for the functional requirements. The tests are written in order to check if the application behaves as expected.

Stress Testing:
The application is tested against heavy load such as complex numerical values, large number of inputs, large number of queries etc. which checks for the stress/load the applications can withstand.

Load Testing:
The application is tested against heavy loads or inputs such as testing of web sites in order to find out at what point the web-site/application fails or at what point its performance degrades.

Ad-hoc Testing:
This type of testing is done without any formal Test Plan or Test Case creation. Ad-hoc testing helps in deciding the scope and duration of the various other testing and it also helps testers in learning the application prior starting with any other testing.

Exploratory Testing:
This testing is similar to the ad-hoc testing and is done in order to learn/explore the application.

Usability Testing:
This testing is also called as ‘Testing for User-Friendliness’. This testing is done if User Interface of the application stands an important consideration and needs to be specific for the specific type of user.

Smoke Testing:
This type of testing is also called sanity testing and is done in order to check if the application is ready for further major testing and is working properly without failing up to least expected level.

Recovery Testing:
Recovery testing is basically done in order to check how fast and better the application can recover against any type of crash or hardware failure etc. Type or extent of recovery is specified in the requirement specifications.

Volume Testing:
Volume testing is done against the efficiency of the application. Huge amount of data is processed through the application (which is being tested) in order to check the extreme limitations of the system.

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