Unit Testing

Unit testing

Unit testing is a test-as-you-go approach in which each significant block of code (i.e. a subroutine, function, event-handler or method) is thoroughly tested before writing any more code that relies on it. Typically, the test will involve single-stepping through the code line by line to determine whether or not it does what it is supposed to do. A unit is the smallest piece of code that can be tested, and should not rely on other code units unless they too have been thoroughly tested (although it is reasonably safe to assume that the library functions provided by an established programming language have already been extensively tested). The aim is to determine whether or not the code has been correctly implemented.

When carrying out unit testing, it is sometimes necessary to comment out statements to prevent the execution of external code – you just need to remember to uncomment the affected statements once testing is complete. Often, a program component consists of several units of code that work together to carry out a specific task. The component may still be considered small enough to qualify as a unit for testing purposes, but care should be taken to ensure that each line of code is executed at least once during testing, although not necessarily in the same test. For example, if a function includes an If..Then..Else statement, a test scenario should be devised for each path of execution.