Test oracle

In computing, software engineering, and software testing, a test oracle (or just oracle) is a mechanism for determining whether a test has passed or failed. The use of oracles involves comparing the output(s) of the system under test, for a given test-case input, to the output(s) that the oracle determines that product should have. The term "test oracle" was first introduced in a paper by William E. Howden. Additional work on different kinds of oracles was explored by Elaine Weyuker. Oracles often operate separately from the system under test. However, method postconditions are part of the system under test, as automated oracles in design by contract models. Determining the correct output for a given input (and a set of program or system states) is known as the oracle problem or test oracle problem, which is a much harder problem than it seems, and involves working with problems related to controllability and observability. A research literature survey covering 1978 to 2012 found several potential categories of test oracles. These oracles are typically associated with formalized approaches to software modeling and software code construction. They are connected to formal specification, model-based design which may be used to generate test oracles, state transition specification for which oracles can be derived to aid model-based testing and protocol conformance testing, and design by contract for which the equivalent test oracle is an assertion. Specified Test Oracles have a number of challenges. Formal specification relies on abstraction, which in turn may naturally have an element of imprecision as all models cannot capture all behavior. A derived test oracle differentiates correct and incorrect behavior by using information derived from artifacts of the system. These may include documentation, system execution results and characteristics of versions of the system under test. Regression test suites (or reports) are an example of a derived test oracle - they are built on the assumption that the result from a previous system version can be used as aid (oracle) for a future system version.