Editing Avionics software (section)

===Unit testing===
"Unit test" code is written to exercise every instruction of the code at least once to get 100% [[code coverage]].  A "coverage" tool is often used to verify that every instruction is executed, and then the test coverage is documented as well, for legal reasons.

This test is among the most powerful.  It forces detailed review of the program logic, and detects most coding, compiler and some design errors.  Some organizations write the unit tests ''before'' writing the code, using the software design as a module specification.  The unit test code is executed, and all the problems are fixed.