Integrate testing.

• Each component should contain a callable operation causing it to check its own invariants (whenever they are computable).
• Screening functions evaluating preconditions should be made part of the interface. For example, an empty function to check if a Stack may be popped.
• Use run-time assertions
• Other tests should be available as part of a module containing the component.
• These operations should be explicitly tied to specifications and documentation, and vice-versa.
• Writing integrated tests is one way to understand and capture previously implicit specifications.
• Self-tests increase consumer confidence in components.