Test oracle: Difference between revisions

Revision as of 20:58, 19 January 2021

Revision as of 20:59, 19 January 2021

Line 3:

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.<ref>Kaner, Cem; [http://www.testingeducation.org/k04/OracleExamples.htm ''A Course in Black Box Software Testing''], 2004</ref> The use of oracles involves comparing the output(s) of the system under test, for a given [[test case|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.<ref>{{cite journal |last1=Howden |first1=W.E. |date=July 1978 |title=Theoretical and Empirical Studies of Program Testing |journal=IEEE Transactions on Software Engineering |volume=4 |issue=4 |pages=293–298 |doi=10.1109/TSE.1978.231514 }}</ref> Additional work on different kinds of oracles was explored by [[Elaine Weyuker]].<ref>Weyuker, Elaine J.; "The Oracle Assumption of Program Testing", in ''Proceedings of the 13th International Conference on System Sciences (ICSS), Honolulu, HI, January 1980'', pp. 44-49</ref>

Oracles often operate separately from the system under test.<ref name="038720881X">Jalote, Pankaj; ''An Integrated Approach to Software Engineering'', Springer/Birkhäuser, 2005, {{ISBN|0-387-20881-X}}</ref> However, [[Method (computer programming)|method]] postconditions are part of the system under test, as automated oracles in [[design by contract]] models.<ref>{{cite journal |last1=Meyer |first1=Bertrand |last2=Fiva |first2=Arno |last3=Ciupa |first3=Ilinca |last4=Leitner |first4=Andreas |last5=Wei |first5=Yi |last6=Stapf |first6=Emmanuel |date=September 2009 |title=Programs That Test Themselves |journal=Computer |volume=42 |issue=9 |pages=46–55 |doi= 10.1109/MC.2009.296 }}</ref> 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,<ref name="Oracle survey"/>{{rp|507}} which is a much harder problem than it seems, and involves working with problems related to controllability and observability.<ref name="ammann-intro">Ammann, Paul; and Offutt, Jeff; "Introduction to Software Testing", ''Cambridge University Press'', 2008, {{ISBN|978-0-521-88038-1}}</ref>

== Categories ==

Line 16:

A derived test oracle differentiates correct and incorrect behaviour by using information derived from artefacts of the system. These may include documentation, system execution results and characteristics of versions of the system under test.<ref name="Oracle survey"/>{{rp|514}} 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. Previously measured performance characteristics may be used as an oracle for future system versions, for example, to trigger a question about observed potential performance degradation. Textual documentation from previous system versions may be used as a basis to guide expectations in future system versions.

A pseudo-oracle<ref name="Oracle survey"/>{{rp|515}} falls into the category of derived test oracle. A pseudo-oracle, as defined by Weyuker,<ref name="pseudo-oracle">{{cite journal |last1=Weyuker |first1=E.J. |date=November 1982 |title=On Testing Non-Testable Programs |journal=The Computer Journal |volume=25 |issue=4 |pages=465–470 |doi=10.1093/comjnl/25.4.465 |doi-access=free }}</ref> is a separately written program which can take the same input as the program/ or system under test so that their outputs may be compared to understand if there might be a problem to investigate.

A partial oracle<ref name="Oracle survey"/>{{rp|515}} is a hybrid between specified test oracle and derived test oracle. It specifies important (but not complete) properties of the system under test. For example, [[metamorphic testing]] exploits such properties, called metamorphic relations, across multiple executions of the system.

Line 23:

An implicit test oracle relies on implied information and assumptions.<ref name="Oracle survey"/>{{rp|518}} For example, there may be some implied conclusion from a program crash, i.e. unwanted behaviour - an oracle to determine that there may be a problem. There are a number of ways to search and test for unwanted behaviour, whether some call it negative testing, where there are specialized subsets such as [[fuzzing]].

There are limitations in implicit test oracles - as they rely on implied conclusions and assumptions. For example, a program/ or process crash may not be a priority issue if the system is a fault-tolerant system and so operating under a form of self-healing/[[self-management (computer science)|self-management]]. Implicit test oracles may be susceptible to false positives due to environment dependencies.

=== Human ===

When specified, derived or implicit test oracles cannot be used, then human input to determine the test oracles is required.<ref name="ammann-intro" /> These can be thought of as quantitative and qualitative approaches.<ref name="Oracle survey"/>{{rp|519–520}} A quantitative approach aims to find the right amount of information to gather on a system under test (e.g., test results) for a stakeholder to be able to make decisions on fit-for-purpose /or the release of the software. A qualitative approach aims to find the representativeness and suitability of the input test data and context of the output from the system under test. An example is using realistic and representative test data and making sense of the results (if they are realistic). These can be guided by [[heuristic]] approaches, such as gut instincts, rules of thumb, checklist aids, and experience to help tailor the specific combination selected for the program/system under test.

== Examples ==

Line 37:

During [[Google]] search, we do not have a complete oracle to verify whether the number of returned results is correct. We may define a metamorphic relation<ref>{{cite journal |first1=Z.Q. |last1=Zhou |first2=S. |last2=Zhang |first3=M. |last3=Hagenbuchner |first4=T.H. |last4=Tse |first5=F.-C. | last5=Kuo |first6=T.Y. |last6=Chen |date=2012 |title=Automated functional testing of online search services |journal=Software Testing, Verification and Reliability |volume=22 |issue=4 |pages=221–243 |doi=10.1002/stvr.437 }}</ref> such that a follow-up narrowed-down search will produce fewer results. This is an example of a partial oracle, which is a hybrid between specified test oracle and derived test oracle.

A statistical oracle uses probabilistic characteristics,<ref>{{cite conference |url=http://www.mathematik.uni-ulm.de/sai/mayer/publications/oracles.pdf |title=Test Oracles Using Statistical Methods |last1=Mayer |first1=Johannes |last2=Guderlei |first2=Ralph |date=2004 |publisher=Springer |book-title=Proceedings of the First International Workshop on Software Quality, Lecture Notes in Informatics |pages=179–189 |conference=First International Workshop on Software Quality}}</ref> for example with image analysis where a range of certainty/ and uncertainty is defined for the test oracle to pronounce a match or otherwise. This would be an example of a quantitative approach in human test oracle.

A heuristic oracle provides representative or approximate results over a class of test inputs.<ref>Hoffman, Douglas; [http://www.softwarequalitymethods.com/Papers/STQE%20Heuristic.pdf Heuristic Test Oracles], Software Testing & Quality Engineering Magazine, 1999</ref> This would be an example of a qualitative approach in human test oracle.