Test Fixture
The prepared data or state a test runs against.
A test fixture is the prepared input a test needs: a sample record, a rendered document, a seeded database, a drawn image. Fixtures are where a surprising number of tests go quietly wrong, because a fixture chosen for convenience can make an assertion meaningless.
The failure has a general shape: the fixture already satisfies the property being asserted, for reasons unrelated to the code. A layout test using an image wider than its container passes whether or not the layout code works, because a shrink-to-fit box and a spanning box produce the same width in that case. Drawing a deliberately narrow fixture makes the two outcomes different, and the assertion real. A scroll test in a container with no height constraint passes vacuously. See Vacuous Truth.
Two further notes. Fixtures should be local and deterministic where the assertion is about behavior — a remote image introduces network variance and decode noise into what should be a pure comparison. And a helper that merges overrides into a base fixture must merge before pruning explicitly-absent keys, or every attempt to blank a field silently keeps the base value and every negative-path test becomes a happy path.
See also10
Test Double
A stand-in for a real dependency during a test — and the ways a stand-in can lie.
Testing & Verification18 connections
Seed Data
Initial content created programmatically to make an empty system usable or demonstrable.
Data & Content14 connections
Visual Regression Testing
Comparing rendered output against a stored baseline to catch unintended visual change.
Testing & Verification14 connections
Record and Replay Testing
Capturing a real interaction once and replaying it deterministically in later test runs.
Agents & Language Models14 connections
Integration Test
A test exercising several components together, through real interfaces rather than doubles.
Testing & Verification17 connections
Unit Test
A fast, isolated test of one unit of behavior with its collaborators replaced.
Testing & Verification25 connections
Nondeterminism
The property that identical inputs may produce different outputs, and what it costs to test around.
Agents & Language Models24 connections
Determinism
The property that identical inputs produce identical outputs, and the foundation of caching and verification.
Systems & Tooling61 connections
Test Isolation
The property that each test passes or fails on its own, regardless of which other tests run, in what order, or in parallel.
Testing & Verification20 connections
Test Data Builder
Helpers that build valid test objects from sensible defaults so each test states only the fields it cares about, and the Object Mother pattern they grew out of.
Testing & Verification9 connections
Linked from13
- Component StoryTesting & Verification
An isolated rendered instance of a component, usable as documentation, a workbench, and a test.
- End-to-End TestTesting & Verification
A test that drives the whole running system the way a user would, from the interface down through every real dependency, buying the most confidence at the highest cost.
- Headless BrowserTesting & Verification
A real browser driven programmatically without a visible window.
- Integration TestTesting & Verification
A test exercising several components together, through real interfaces rather than doubles.
- Property-Based TestingTesting & Verification
Asserting a general property that should hold for all inputs, then letting the framework generate many random inputs to try to break it.
- Record and Replay TestingAgents & Language Models
Capturing a real interaction once and replaying it deterministically in later test runs.
- Responsive BreakpointDesign & Interface
A viewport width at which a layout changes, and the assumptions that come with it.
- Seed DataData & Content
Initial content created programmatically to make an empty system usable or demonstrable.
- Test Data BuilderTesting & Verification
Helpers that build valid test objects from sensible defaults so each test states only the fields it cares about, and the Object Mother pattern they grew out of.
- Test DoubleTesting & Verification
A stand-in for a real dependency during a test — and the ways a stand-in can lie.
- Test IsolationTesting & Verification
The property that each test passes or fails on its own, regardless of which other tests run, in what order, or in parallel.
- Unit TestTesting & Verification
A fast, isolated test of one unit of behavior with its collaborators replaced.
- Visual Regression TestingTesting & Verification
Comparing rendered output against a stored baseline to catch unintended visual change.