Boundary value analysis is the technique of making sure that behavior of system is predictable for the input and output boundary conditions. Reason why boundary conditions are very important for testing is because defects could be introduced at the boundaries very easily. For example, if you were to write code to simulate following condition -

"Input should be greater than equal to 10 and less than 50"

• input >10 AND input Input value 10 in invalid now.
• input <=10 AND input Input value 9 is valid now.
• input >=10 AND input Input value 50 is valid now
• input >=10 AND input >50 -----> Input value 49 is invalid now

Because it is very easy to introduce defects at boundaries, boundary values are important. So for the above example, at the minimum we should have following test cases for boundaries

9, 10, 11 and 48, 49, 50

As a general rule, if you have any input field it should be tested with following set of data at the minimum.

lower_boundary - 1, lower_boundary, lower_boundary + 1 and upper_boundary - 1, upper_boundary, upper_boundary + 1

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Desktop application runs on personal computers and work stations, so when you test the desktop application you are focusing on a specific environment. You will test complete application broadly in categories like GUI, functionality, Load, and backend i.e DB.

In client server application you have two different components to test. Application is loaded on server machine while the application exe on every client machine. You will test broadly in categories like, GUI on both sides, functionality, Load, client-server interaction, backend. This environment is mostly used in Intranet networks. You are aware of number of clients and servers and their locations in the test scenario.

Web application is a bit different and complex to test as tester don’t have that much control over the application. Application is loaded on the server whose location may or may not be known and no exe is installed on the client machine, you have to test it on different web browsers. Web applications are supposed to be tested on different browsers and OS platforms so broadly Web application is tested mainly for browser compatibility and operating system compatibility, error handling, static pages, backend testing and load testing.

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