This type of testing relies heavily on walk throughs, inspection, and formal verification. The programmers are not allowed to test any of their code by executing the code other than doing some syntax testing using a compiler. The software development philosophy is based on avoiding software defects by using a rigorous inspection process. The objective of this software is zero-defect software. The name ‘clean room’ was derived from the analogy with semi-conductor fabrication units. In these units (clean rooms), defects are avoided by manufacturing in ultra-clean atmosphere. In this kind of development, inspections to check the consistency of the components with their specifications has replaced unit-testing.
This technique reportedly produces documentation and code that is more reliable and maintainable than other development methods relying heavily on code execution-based testing.
The clean room approach to software development is based on five characteristics:
- Formal specification: The software to be developed is formally specified. A state-transition model which shows system responses to stimuli is used to express the specification.
- Incremental development: The software is partitioned into increments which are developed and validated separately using the clean room process. These increments are specified, with customer input, at an early stage in the process.
- Structured programming: Only a limited number of control and data abstraction constructs are used. The program development process is process of stepwise refinement of the specification.
- Static verification: The developed software is statically verified using rigorous software inspections. There is no unit or module testing process for code components
- Statistical testing of the system: The integrated software increment is tested statistically to determine its reliability. These statistical tests are based on the operational profile which is developed in parallel with the system specification. The main problem with this approach is that testing effort is increased as walk throughs, inspection, and verification are time-consuming.