Two heuristics of Software testing : Visibility and Control

Software testability is how easily, completely and conveniently a computer program can be tested. Software engineers design a computer product, system or program keeping in mind the product testability. Good programmers are willing to do things that will help the testing process and a checklist of possible design points, features and so on can be useful in negotiating with them.
Visibility has already been discussed.

Control refers to our ability to provide inputs and reach states in the software under test. The features to improve controllability are:
- Test Points: Allows the data to be inspected, inserted or modified at points in the software. It is especially useful for data-flow applications. In addition, a pipe and filters architecture provides many opportunities for test points.

- Custom User Interface Controls: Custom UI controls often raise serious testability problems with GUI test drivers. Ensuring testability usually requires adding methods to report necessary information, customizing test tools to make use of these methods, getting a tool expert to advise developers on testability and to build the required support and asking the third party control vendors regarding support by test tools.

- Test Interfaces: Interfaces may be provided specifically for testing e.g. Excel and Xconq etc.Existing interfaces may be able to support significant testing e.g. InstallShield, AutoCad, Tivoli etc.

- Fault Injection: Error seeding, instrumenting low level input/output code to simulate errors makes it much easier to test error handling. It can be handled at both system and application level.

- Installation and Setup: Testers should be notified when installation has completed successfully. They should be able to verify installation, pro grammatically create sample records and run multiple clients, daemons or servers on a single machine.