> ## Glossary

> Fetch the complete documentation index at: https://antithesis.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

---

Every Antithesis-specific term we use  in the docs is collected and alphabetized here. We also have a [distributed systems reliability glossary](/docs/resources/reliability_glossary/) that covers terms used in this space more broadly.

Assertion
: A way to express [properties](#property) programmatically so Antithesis can test them. Unlike the assertions you know from unit testing, they don't stop execution when they fail. Covered in depth [here](/docs/concepts/properties_assertions/assertions/).

Assertion catalog
: Antithesis registers every [assertion](#assertion) added in the [system under test](#system-under-test-sut) and the [workload](#workload) in an assertion catalog, which it uses to evaluate the corresponding [properties](#property).

Autonomous testing
: Using software to generate test cases, instead of a human developer. Covered in depth [here](/docs/resources/autonomous_testing/).

Branch
: A portion of a timeline downstream of a particular fork in the multiverse map. Generally used in the sense of “a particular event created a new branch.” Covered in depth [here](/docs/product/logs_explorer/#the-multiverse-map).

Default properties
: Antithesis comes with a built-in set of [properties](#property) that should hold in all systems.

Deterministic simulation testing
: Testing a system by running it in an environment simulating some or all layers of the testing stack. Sources of non-determinism like clocks, thread interleaving, and system-provided sources of randomness (among others), are made deterministic in the test environment. Covered in depth [here](/docs/resources/deterministic_simulation_testing/).

Event
: An occurrence within the [simulation](#deterministic-simulation-testing). Commonly, a log message from your system, an SDK assertion, or a fault event that Antithesis triggered. Every event occurs at a unique [moment](#moment).

Example-based testing
: Tests which dictate the inputs to be applied to the [system under test](#system-under-test-sut), and expect a specific result. This is the approach taken by most software testing.

Moment
: Used as in common English, a unit of time on a [timeline](#timeline). Each moment occurs on a particular timeline, and there are some moments where no events occur.

Multiverse
: The collection of [timelines](#timeline) explored during a single test run. You can think of each test run as producing its own multiverse.

Property
: An invariant. A promised or expected behavior of a system that we want to test. Covered in depth [here](/docs/concepts/properties_assertions/properties/).

Property-based testing
: Testing that uses computer-generated random inputs to check that a function or system behaves as expected under a wide range of conditions. Covered in depth [here](/docs/resources/property_based_testing/).

Setup
: The initial phase of the test run when your [system under test](#system-under-test-sut) and your [workload](#workload) are deployed and made ready for exploration.

System under test (SUT)
: The system you're testing.

Test environment
: AKA “the Antithesis environment” or just “the environment.” The deterministic simulation environment where the [SUT](#system-under-test-sut) is deployed and run during the test.

Test run
: AKA "run". A single testing session in Antithesis, during which multiple [timelines](#timeline) are explored. A single test run generates a single [multiverse](#multiverse).

Timeline
: One complete execution history, from start to end, that your system took during the [test run](#test-run). [Exploring your software](/docs/introduction/how_antithesis_works/#exploring-your-software) explains this concept in detail.

Triage report
: A report consolidating the results at the end of a [test run](#test-run).

Virtual time
: The simulated clock used to order events during a [test run](#test-run).

Workload
: Code that drives activity in your system during an [test run](#test-run). Antithesis observes the system behavior to detect failures.