We may also be required to carry out software testing to meet contractual or legal requirements, or industry –specific standards. These standards may specify what type of techniques we must use, or the percentage of the software code that must be exercised . It may by a surprise to learn that we don’t always test all the code; that would be too expensive compared with the risk we are trying deal with. However – as we’d expect – the higher the risk associated with the Indus-try using the software, the more likely it is that a standard for testing will exist. The avionics, motor, motor, medical and pharmaceutical industries all have standards covering the testing of software. For example, the US Federal Aviation Administration’s DO-178B standard [RTCA/DO-178B] has requirements for test coverage.