Bevy testing patterns (docs-first stub)
Not a full port. Tests here are Cargo's test harness. There is no GdUnit twin.
When to use
Load this when a Bevy crate needs unit or integration tests. The Cargo book page for cargo test (opened 2026-10-11) is the source. A current Bevy "how to App::update inside #[test]" page was not opened, so that recipe stays a gap.
ECS shape
- Command:
cargo testcompiles and runs unit tests, integration tests, and documentation tests.cargo test name_filterruns names that contain the filter. Arguments after--go to libtest (cargo test -- --help). - What runs: functions annotated with
#[test]. The harness runs them in multiple threads. The working directory for each test is the package root, so relative paths resolve from that root no matter where you invoked Cargo. - Scope: default
cargo testcovers the lib, bins as unit tests, integration tests, and doc tests, and it builds examples.--liblimits to the library.harness = falseon a target means you supplymain. - Profile: the
testprofile is the default.--profile=debugkeeps debug info.-- --no-captureshows test output. - Bevy types inside a test: not specified here. Do not copy an
App::new()test from an old discussion. Bevy's own crates contain#[cfg(test)]modules; their helpers were not opened as a public guide.
Godot idea to Bevy idiom
| Idea | Bevy idiom (idea only) |
|---|---|
| Run the suite | cargo test from the package |
| One test name | cargo test name_filter |
| See prints | cargo test -- --no-capture |
| Scene-tree test runner | No twin. GdUnit stays on the Godot skill |
Gaps
- No docs.rs
latestpage was opened that showsApp,MinimalPlugins, andapp.update()inside#[test]. Do not invent that harness. - Headless frame capture, golden images, and input injection for tests were not opened.
- Doctest working-directory rules differ from unit tests (workspace root for
rustdoccompile). Do not assume a doctest can readassets/the same way.
Expert Knowledge Delta
Library target in prose: Bevy 0.20.0. Lattice URLs stay unversioned.
Opened canon only: Component, Resource, Query, Commands, Startup, Update, Fixed / FixedMain (bevy::time), .chain(), Plugin, DefaultPlugins, MinimalPlugins. Messages and observers are an ownership slot. This file does not invent their struct APIs. Systems run in parallel unless .chain() orders the ones that conflict.
Who owns state
| Piece | Owner | Who may mutate | Schedule |
|---|---|---|---|
| Data on one entity | Component | One system via Query | Update or FixedMain |
| One value for the whole app | Resource | One system | Startup to insert, then the schedule that reads it |
| Spawn | Commands | The spawning system | Startup for the initial world; later schedules for runtime spawn |
| Order that must not race | .chain() | The chained systems only | Same schedule |
| Plugin boundary | Plugin | build registers systems and resources | Before the app runs |
Borrow rule: two systems that both mutably query the same component must be ordered (.chain()) or split so only one writes. Unrelated systems stay parallel. That is the ECS page rule, not a guess at a system-set API.
Decision
| If you need | Do this | Do not |
|---|---|---|
| Per-entity data | Component + Query | A Godot node script |
| App-wide config or clock | Resource | Copy the value onto every entity |
| Stable simulation step | FixedMain and the Fixed clock | Tie simulation to raw frame Update |
| Startup spawn | Commands in Startup | Spawn from a render system |
| Cross-system notice that is not shared state | Message or observer slot in bevy-events-messaging | A new event type invented in this file |
| An API this skill did not open | A Gaps row | A fabricated crate (solver, navmesh module, net, XR) |
Load references/a-gate-notes.md for the same table plus the gap rule.
NEVER
-
Do not put
/0.20.0/in lattice URLs. WHY: permalinks stay onlatest. The 0.20.0 pin belongs in prose once. -
Do not mutably query the same component from two unordered systems. WHY: the schedule runs systems in parallel unless
.chain()orders them. -
Do not invent a physics, navigation, networking, or XR crate here. WHY: those rows are gaps, blocked, or revisit.
-
No GdUnit, GUT, or Godot test-runner types. WHY: a Godot port, an unopened API, or a public lie fails the docs-first bar.
-
No
App::updatetest recipe this file did not open. WHY: a Godot port, an unopened API, or a public lie fails the docs-first bar. -
No third-party Bevy test crates. WHY: a Godot port, an unopened API, or a public lie fails the docs-first bar.
-
No Creation Station content. WHY: a Godot port, an unopened API, or a public lie fails the docs-first bar.
-
No umbrella skill over Godot and Bevy. WHY: a Godot port, an unopened API, or a public lie fails the docs-first bar.
-
Do not mark this row
ported. It isdocs_mapped. WHY: a Godot port, an unopened API, or a public lie fails the docs-first bar.
Reference
docs.rs links use the unversioned latest permalink. The library pin on bevy-master stays 0.20.0.
Official Documentation
- Migration guides - Unversioned hop index.
- bevy crate - Unversioned API index.
- cargo test -
#[test], filters, libtest args, package root as cwd. - Examples - Example tree on the
latestbranch. Examples are not the test harness.
Related Skills
Prerequisites
- bevy-master - Who owns which piece of state.
- bevy-project-foundations - The Cargo package
cargo testruns against.
Complements
- godot-testing-patterns - Godot counterpart. GdUnit stays there.
Downstream / consumers
- None yet.
Master
- bevy-master - Bevy router.


