A key step in the process of software engineering is testing the software for correct behavior prior to release to end users.

For small scale engineering efforts (including prototypes), exploratory testing may be sufficient. With this informal approach, the tester does not follow any rigorous testing procedure, but rather explores the user interface of the application using as many of its features as possible, using information gained in prior tests to intuitively derive additional tests. The success of exploratory manual testing relies heavily on the domain expertise of the tester, because a lack of knowledge will lead to incompleteness in testing. One of the key advantages of an informal approach is to gain an intuitive insight to how it feels to use the application.

Large scale engineering projects that rely on manual software testing follow a more rigorous methodology in order to maximize the number of defects that can be found. A systematic approach focuses on predetermined test cases and generally involves the following steps.

Choose a high level test plan where a general methodology is chosen, and resources such as people, computers, and software licenses are identified and acquired.
Write detailed test cases, identifying clear and concise steps to be taken by the tester, with expected outcomes.
Assign the test cases to testers, who manually follow the steps and record the results.
Author a test report, detailing the findings of the testers. The report is used by managers to determine whether the software can be released, and if not, it is used by engineers to identify and correct the problems.

A rigorous test case based approach is often traditional for large software engineering projects that follow a Waterfall model. However, at least one recent study did not show a dramatic difference in defect detection efficiency between exploratory testing and test case based testing.

Testing can be through black-, white- or grey-box testing. In white-box testing the tester is concerned with the execution of the statements through the source code. In black-box testing the software is run to check for the defects and is less concerned with how the processing of the input is done. Black-box testers do not have access to the source code. Grey-box testing is concerned with running the software while having an understanding of the source code and algorithms.

Static and dynamic testing approach may also be used. Dynamic testing involves running the software. Static testing includes verifying requirements, syntax of code and any other activities that do not include actually running the code of the program.

Testing can be further divided into functional and non-functional testing. In functional testing the tester would check the calculations, any link on the page, or any other field which on given input, output may be expected. Non-functional testing includes testing performance, compatibility and fitness of the system under test, its security and usability among other things.