Integration Testing and System Testing

Integration Testing

Integration testing is a systematic technique for constructing the program structure while at the same time conducting tests to uncover errors associated with interfacing. In this, many unit tested modules are combined into subsystems, which are then tested. The goal here is to see if the modules can be integrated properly. Hence, the emphasis is on testing interfaces between modules. This testing activity can be considered testing the design.
A major problem that arises during integration testing is localising errors. There are complex interactions between the system components and, when an anomalous output is discovered, you may find it hard to identify where the error occurred. To make it easier to locate errors, you should always use an incremental approach to system integration and testing. Initially, you should integrate a minimal system configuration and test this system. You then add components to this minimal configuration and test after each added increment.

Figure st.02 Incremental Integration Testing
In the example shown in Figure st.02, A, B, C and D are components and T1 to T5 are related sets of tests of the features incorporated in the system. T1, T2 and T3 are first run on a system composed of component A and component B (the minimal system). If these reveal defects, they are corrected. Component C is integrated and T1, T2 and T3 are repeated to ensure that there have not been unexpected interactions with A and B. If problems arise in these tests, this probably means that they are due to interactions with the new component. The source of the problem is localised, thus simplifying defect location and repair. Test set T4 is also run on the system. Finally, component D is integrated and tested using existing and new tests (T5).

System Testing

Here the entire software system is tested. The reference document for this process is the requirements document, and the goal is to see if the software meets its requirements. This is often a large exercise, which for large projects may last many weeks or months. This is essentially a validation exercise, and in many situations it is the only validation activity. The testing process is concerned with finding errors that result from unanticipated interactions between subsystems and system components. It is also concerned with validating that the system meets its functional and non-functional requirements. There are essentially three main kinds of system testing

• Alpha Testing. Alpha testing refers to the system testing carried out by the test team within the development organization. The alpha test is conducted at the developer’s site by the customer under the project team’s guidance. In this test, users test the software on the development platform and point out errors for correction. However, the alpha test, because a few users on the development platform conduct it, has limited ability to expose errors and correct them. Alpha tests are conducted in a controlled environment. It is a simulation of real-life usage. Once the alpha test is complete, the software product is ready for transition to the customer site for implementation and development.
• Beta Testing. Beta testing is the system testing performed by a selected group of friendly customers. If the system is complex, the software is not taken for implementation directly. It is installed and all users are asked to use the software in testing mode; this is not live usage. This is called the beta test. In this test, end users record their observations, mistakes, errors, and so on and report them periodically. In a beta test, the user may suggest a modification, a major change, or a deviation. The development has to examine the proposed change and put it into the change management system for a smooth change from just developed software to a revised, better software. It is standard practice to put all such changes in subsequent version releases.
• Acceptance Testing. Acceptance testing is the system testing performed by the customer to determine whether to accept or reject the delivery of the system. When customer software is built for one customer, a series of acceptance tests are conducted to enable the customer to validate all requirements. Conducted by the end-user rather than the software engineers, an acceptance test can range from an informal ‘test drive’ to a planned and systematically executed series of tests. In fact, acceptance testing can be conducted over a period of weeks or months, thereby uncovering cumulative errors that might degrade the system over time.

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