|This article does not cite any references or sources. (July 2009)|
A test case in software engineering is a set of conditions or variables under which a tester will determine whether an application or software system is working correctly. The mechanism for determining whether a software program or system has passed or failed such a test is known as a test oracle. In some settings, an oracle could be a requirement or use case, while in others it could be a heuristic. It may take many test cases to determine that a software program or system is considered sufficiently scrutinized to be released. Test cases are often referred to as test scripts, particularly when written. Written test cases are usually collected into test suites.
Formal test cases 
In order to fully test that all the requirements of an application are met, there must be at least two test cases for each requirement: one positive test and one negative test. If a requirement has sub-requirements, each sub-requirement must have at least two test cases. Keeping track of the link between the requirement and the test is frequently done using a traceability matrix. Written test cases should include a description of the functionality to be tested, and the preparation required to ensure that the test can be conducted.
A formal written test-case is characterized by a known input and by an expected output, which is worked out before the test is executed. The known input should test a precondition and the expected output should test a postcondition.
Informal test cases 
For applications or systems without formal requirements, test cases can be written based on the accepted normal operation of programs of a similar class. In some schools of testing, test cases are not written at all but the activities and results are reported after the tests have been run.
In scenario testing, hypothetical stories are used to help the tester think through a complex problem or system. These scenarios are usually not written down in any detail. They can be as simple as a diagram for a testing environment or they could be a description written in prose. The ideal scenario test is a story that is motivating, credible, complex, and easy to evaluate. They are usually different from test cases in that test cases are single steps while scenarios cover a number of steps of the key.
Typical written test case format 
A test case is usually a single step, or occasionally a sequence of steps, to test the correct behaviour/functionality, features of an application. An expected result or expected outcome is usually given.
Additional information that may be included:
- test case ID
- test case description
- test step or order of execution number
- related requirement(s)
- test category
- check boxes for whether the test can be or has been automated
Larger test cases may also contain prerequisite states or steps, and descriptions.
A written test case should also contain a place for the actual result.
These steps can be stored in a word processor document, spreadsheet, database or other common repository.
In a database system, you may also be able to see past test results and who generated the results and the system configuration used to generate those results. These past results would usually be stored in a separate table.
Test suites often also contain
- Test summary
Besides a description of the functionality to be tested, and the preparation required to ensure that the test can be conducted, the most time consuming part in the test case is creating the tests and modifying them when the system changes.
Under special circumstances, there could be a need to run the test, produce results, and then a team of experts would evaluate if the results can be considered as a pass. This happens often on new products' performance number determination. The first test is taken as the base line for subsequent test / product release cycles.
Acceptance tests, which use a variation of a written test case, are commonly performed by a group of end-users or clients of the system to ensure the developed system meets the requirements specified or the contract. User acceptance tests are differentiated by the inclusion of happy path or positive test cases to the almost complete exclusion of negative test cases.
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