Software Testing notes

"If debugging is the process of removing software bugs, then programming must be the process of putting them in." - Dijkstra
It sure is safe to say that software is ubiquitous and touches almost everyone on this planet either directly or otherwise. The software we help produce has the potential for wide reaching impact. A chief determinant of the nature of impact, whether positive or negative, hinges on the quality of the software we produce. Testing directly contributes to improving quality of software by way of detecting defects and enabling these to be addressed before the product ships.

When defects are not detected and consequently left un-addressed, failures result during operation of the software. These failures can have significant cost implications for the producer of the software which may include (and not restricted to) costs to address these issues that are reported back from customers and issue patches, loss of customer confidence and credibility, loss or corruption of data which in turn has potential for causing much damage, legal implications due to failure or non-compliance, and many other repercussions which are best avoided by taking pro-active steps to prevent and eliminate defects during software production. A relatively smaller investment in preventing software defects from shipping out helps to avoid spending a much larger amount later, on handling the consequences of those defects.

So, what is the purpose of testing? We may summarize the purpose of testing into the following three points.

1.    To validate conformance of the software to the business requirements
2.    To verify conformance of the software to the design and specifications
3.    To find errors

An important element in finding errors is timing. The sooner in the development cycle when errors are detected, the less expensive it is to fix them. Studies show that the longer errors remain undetected across the development life cycle, the greater is the cost of fixing these later. Different statistics provide varying estimates of cost involved in fixing defects at different stages of software development, testing and deployment. However, all of them agree that the cost is least for defects identified during the initial requirements stage, increasing thereon for every subsequent stage such as design, implementation, testing and the highest for defects found after the product has shipped. For example, an estimate of the cost of fixing defects post release is said to be over 40 times the cost of fixing them at the requirements stage. 

The point here is that for software testing to be of greater value to the business, testing must not be relegated to the fag end of the development life cycle to come in only post implementation. The earlier you have testing engaged, the greater the defects that may be prevented from being carried over across development phases and lesser the cost to address them.