A test fixture is a device used to consistently test some item, device, or piece of software. Test fixtures are used in the testing of electronics, software and physical devices.

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 smart fixture.

Test fixtures can come in different shapes, sizes, and functions. There are several different types of test fixtures, including In-Circuit Test Fixtures, Functional Test Fixtures, and Wireless Test Fixtures. In Circuit Test (ICT) fixtures individually test each component on a PCB, while functional test fixtures assess the entire board's functionality. Functional test fixtures simulate real-world conditions, whereas ICT is more focused on detecting assembly defects like short circuits or missing components. An In-Circuit Test fixture can come in both Inline and Standard variations. An Inline Test Fixture is designed for fast, automated testing directly within a production line, ideal for high-volume manufacturing where continuous testing maximises efficiency. A Standard Test Fixture, on the other hand, usually requires manual loading, making it well-suited to smaller-scale or specialised testing.

In the context of software, a test fixture (also called "test context")^{[citation needed]} is used to set up the system state and input data needed for test execution. 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. In most cases, a custom test fixture will normally require custom test software. This software is created in order to ensure optimal testing performance and seamless integration. The custom software can be configured to carry out a number of different tests from BIST (Built-In Self Test) to advanced JTAG Implementation.

Test fixtures can be set up three different ways: in-line, delegate, and implicit.

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.

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.