Topic: Test Levels

    * Unit testing tests the minimal software component and sub-component or modules by the programmers.
    * Integration testing exposes defects in the interfaces and interaction between integrated components(modules).
    * Functional testing tests the product according to programmable work.
    * System testing tests an integrated system to verify/validate that it meets its requirements.
    * Acceptance testing testing can be conducted by the client. It allows the end-user or customer or client to decide whether or not to accept the product. Acceptance testing may be performed after the testing and before the implementation phase. See also Development stage
          o Alpha testing is simulated or actual operational testing by potential users/customers or an independent test team at the developers' site. Alpha testing is often employed for off-the-shelf software as a form of internal acceptance testing, before the software goes to beta testing.
          o Beta testing comes after alpha testing. Versions of the software, known as beta versions, are released to a limited audience outside of the company. The software is released to groups of people so that further testing can ensure the product has few faults or bugs. Sometimes, beta versions are made available to the open public to increase the feedback field to a maximal number of future users.

It should be noted that although both Alpha and Beta are referred to as testing it is in fact use emersion. The rigors that are applied are often unsystematic and many of the basic tenants of testing process are not used. The Alpha and Beta period provides insight into environmental and utilization conditions that can impact the software.

After modifying software, either for a change in functionality or to fix defects, a regression test re-runs previously passing tests on the modified software to ensure that the modifications haven't unintentionally caused a regression of previous functionality. Regression testing can be performed at any or all of the above test levels. These regression tests are often automated.