The standard testing approach in software systems comprises of the sequence of steps as represented in the following diagram.

In each stage a set of tests are executed, and the results are reviewed. Based on the review, further steps are taken until all the stages are completed.

Starting with Unit Testing by the developers, the application needs to go through the system testing, system integration testing, and User Acceptance Testing (UAT), respectively. Moreover, the technical tests such as load performance testing and failover tests should definitely be included in the test plan.