Component Testing
Starting from the bottom the first test level is "Component Testing", sometimes called Unit Testing. It involves checking that each feature specified in the "Component Design" has been implemented in the component.
In theory an independent tester should do this, but in practise the developer usually does it, as they are the only people who understand how a component works. The problem with a component is that it performs only a small part of the functionality of a system, and it relies on co-operating with other parts of the system, which may not have been built yet. To overcome this, the developer either builds, or uses special software to trick the component into believing it is working in a fully functional system.
Interface Testing
As the components are constructed and tested they are then linked together to check if they work with each other. It is a fact that two components that have passed all their tests, when connected to each other produce one new component full of faults. These tests can be done by specialists, or by the developers.
Interface Testing is not focussed on what the components are doing but on how they communicate with each other, as specified in the "System Design". The "System Design" defines relationships between components, and this involves stating:
- What a component can expect from another component in terms of services.
- How these services will be asked for.
- How they will be given.
- How to handle non-standard conditions, i.e. errors.
Tests are constructed to deal with each of these.
The tests are organised to check all the interfaces, until all the components have been built and interfaced to each other producing the whole system.
System Testing
Once the entire system has been built then it has to be tested against the "System Specification" to check if it delivers the features required. It is still developer focussed, although specialist developers known as systems testers are normally employed to do it.
In essence System Testing is not about checking the individual parts of the design, but about checking the system as a whole. In effect it is one giant component.
System testing can involve a number of specialist types of test to see if all the functional and non-functional requirements have been met. In addition to functional requirements these may include the following types of testing for the non-functional requirements:
- Performance - Are the performance criteria met?
- Volume - Can large volumes of information be handled?
- Stress - Can peak volumes of information be handled?
- Documentation - Is the documentation usable for the system?
- Robustness - Does the system remain stable under adverse circumstances?
There are many others, the needs for which are dictated by how the system is supposed to perform.
Acceptance Testing
Acceptance Testing checks the system against the "Requirements". It is similar to systems testing in that the whole system is checked but the important difference is the change in focus:
- Systems Testing checks that the system that was specified has been delivered.
- Acceptance Testing checks that the system delivers what was requested.
The customer, and not the developer should always do acceptance testing. The customer knows what is required from the system to achieve value in the business and is the only person qualified to make that judgement. To help them courses and training are available.
The forms of the tests may follow those in system testing, but at all times they are informed by the business needs.
Release Testing
Even if a system meets all its requirements, there is still a case to be answered that it will benefit the business. The linking of "Business Case" to Release Testing is looser than the others, but is still important.
Release Testing is about seeing if the new or changed system will work in the existing business environment. Mainly this means the technical environment, and checks concerns such as:
- Does it affect any other systems running on the hardware?
- Is it compatible with other systems?
- Does it have acceptable performance under load?
These tests are usually run the by the computer operations team in a business. The answers to their questions could have significant a financial impact if new computer hardware should be required, and adversely affect the "Business Case".
It would appear obvious that the operations team should be involved right from the start of a project to give their opinion of the impact a new system may have. They could then make sure the "Business Case" is relatively sound, at least from the capital expenditure, and ongoing running costs aspects. However in practise many operations teams only find out about a project just weeks before it is supposed to go live, which can result in major problems.
Regression Tests
With modern systems one person's system, becomes somebody else's component. It follows that all the above types of testing could be repeated at many levels in order to deliver the final value to the business. In fact every time a system is altered.
