What is code coverage ?

People know what software testing is, and most people in the profession can differentiate between white box and black box testing. However, when you get into more details, and look to identify how testing can provide even greater value, the benefit of measures such as code coverage become apparent. At the same time, there would be a large number of software professionals who are not even aware of what code coverage is, and what are its key benefits. So the idea of this article is to try and articulate some of the benefits.
So what is Code Coverage ?
Well, Code coverage is a type of measure used in software testing which tries to answer the questions about the degree to which the entire source code of an application has been tested. Traditional black box testing, with its focus on functional testing cannot even come close to trying to answer this question, although White Box testing does come closer to trying to answer this question. In fact, if you examine code coverage practices in detail, it is possible to say that code coverage is a form of testing that inspects the code directly and is therefore a form of white box testing.
Code coverage techniques were amongst the first techniques invented for answering the question of systematic software testing. For those proponents of the text plan / case based method of testing, code coverage testing works on the principle that it is entirely possible that sections of a software application remain untouched by test data, and as a result, then it is not possible to say, with any degree of certainty, that these sections do not contain residual errors.
How do you go ahead with actually trying to do code coverage ?
Code Coverage requires support from engineering to proceed. Why is this so ? Getting code coverage in practise requires a different procedure from the normal software build - The target application / software is configured to be built with special options / libraries and/or run under a special environment such that every function that is exercised (executed) in the program(s) is mapped back to the function points in the source code. Doing this systematic process (although requires effort and the value does not seem immediately clear to individual developed and QE) allows developers and quality assurance personnel to look for parts of a system that are rarely or never accessed under normal conditions (error handling and the like) and helps reassure test engineers that the most important conditions (function points) have been tested. Once this exercise has been done, the output is further analysed to see what areas of code have not been exercised and the tests are updated to include these areas as necessary. Once this exercise has been completed (and it may need to be done on a regular basis as the code is in the process of being developed), it gives a much higher level of confidence about the overall quality of the code.