Test fixture
A test fixture is an environment used to consistently test some item, device, or piece of software. Test fixtures can be found when testing electronics, software and physical devices. Electronics. In testing electronic equipment such as circuit boards, electronic components, and chips, a test fixture is a device or setup designed to hold the device under test in place and allow it to be tested by being subjected to controlled electronic test signals. Examples are a bed of nails tester or SmartFixture. Software. A software test fixture sets up a system for the software testing process by initializing  it, thereby satisfying any preconditions the system may have. For example, the Ruby on Rails web framework uses YAML to initialize a database with known parameters before running a test. This allows for tests to be repeatable, which is one of the key features of an effective test framework. Setup. Test fixtures can be set up three different ways: in-line, delegate, and implicit. Advantages and disadvantages. The main advantage of a test fixture is that it allows for tests to be repeatable since each test is always starting with the same setup. Test fixtures also ease test code design  by allowing the developer to separate methods into different functions and reuse each function for other tests. Further, test fixtures preconfigure tests into a known initial state instead of working with whatever was left from a previous test run. A disadvantage is that it could lead to duplication of test fixtures if using in-line setup. Practices to avoid. It is considered bad practice when implicit test fixtures are too general, or when a test method sets up a test fixture and does not use it during the test. A more subtle issue is if the test methods ignore certain  fields within the test fixture. Another bad practice is a test setup that contains more steps than needed for the test; this is a problem seen in in-line setup. A test case is considered "unsafe" when it modifies its fixture(s). An unsafe test case can render subsequent tests useless by leaving the fixture in an unexpected state. It also causes the order of tests to be important: a modified fixture must be reset if more tests are to be run after an unsafe test. Examples. Examples of fixtures include loading a database with a specific known set of data , erasing a hard disk and installing a known clean operating system installation, copying a specific known set of files, or the preparation of input data as well as set-up and creation of mock objects. Software which is used to run reproducible tests systematically on a piece of software under test is known as a test harness; part of its job is to set up suitable test fixtures. In generic xUnit, a "test fixture" is all the things that must be in place in order to run a test and expect a particular outcome. Frequently fixtures are created by handling  setUp() and "tearDown()" events of the unit testing framework. In "setUp()" one would create the expected state for the test and in "tearDown()" it would clean up what had been set up. Four phases of a test: Physical testing. In physical testing, a fixture is a device or apparatus to hold or support the test specimen during the test. The influence of test fixtures on test results is important and is an ongoing subject of research. Many test methods detail the requirements of test fixtures in the text of the document. Some fixtures employ clamps, wedge grips and pincer grips . Further types of construction include eccentric roller fixtures, thread grips and button head grips and rope grips. Mechanical holding apparatuses provide the clamping force via arms, wedges or eccentric wheel to the jaws. Additionally there are pneumatic and hydraulic fixtures for tensile testing that allow very fast clamping procedures and very high clamping forces.