/godot-testing

name: godot-testing
description: Use when writing tests for Godot projects — TDD workflow with GUT and gdUnit4, covers both GDScript and C#

Godot Testing

This skill covers test-driven development (TDD) for Godot 4.3+ projects using GUT (Godot Unit Testing) and gdUnit4. It includes framework selection, full RED-GREEN-REFACTOR examples, test structure, running tests in CI, and common testing patterns.

> **Related skills:** **godot-code-review** for review checklists, **dependency-injection** for test-friendly architecture, **export-pipeline** for CI/CD test automation.

Framework Selection

| Feature | GUT | gdUnit4 | |-----------------------|----------------------------------|-----------------------------------| | Language | GDScript-first, limited C# | GDScript + C# (first-class) | | Install | AssetLib or git submodule | AssetLib or git submodule | | Editor integration | Built-in GUT panel | Built-in inspector + panel | | Mocking | `double()` / `stub()` API | `mock()` / `spy()` API | | Scene testing | `add_child_autofree()` | `auto_free()` + scene runner | | CI support | `gut_cmdln.gd` CLI script | `runtest.sh` / `GdUnitCmdTool.gd` | | C# support | Minimal (GDScript wrappers only) | Native C# assertions + lifecycle | | Maturity | Established (Godot 3 + 4) | Godot 4 focused, actively updated | | Best for | Pure GDScript projects | Mixed GDScript/C# or C#-only |

**Rule of thumb:** Use GUT for GDScript-only projects. Use gdUnit4 for C# projects or when you need first-class C# support and scene runner utilities.

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TDD Workflow: RED-GREEN-REFACTOR

The standard Test-Driven Development cycle: write a failing test (RED), write minimal code to pass (GREEN), then refactor without breaking the test. Each step has its own discipline — don't skip RED (you'll write tests that pass trivially), and don't skip REFACTOR (technical debt compounds).

> See [references/tdd-workflow.md](references/tdd-workflow.md) for a worked GDScript + C# example walking through all three steps on a HealthComponent.

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Test Directory Structure

res://
├── .gutconfig.json                       # GUT default config file (optional)
├── src/
│   └── components/
│       ├── health_component.gd
│       └── HealthComponent.cs
└── tests/
    ├── unit/
    │   ├── test_health_component.gd      # GUT: test_ prefix (default -gprefix)
    │   └── HealthComponentTest.cs        # gdUnit4 C#: [TestSuite] attribute
    └── integration/
        ├── test_player_scene.gd
        └── PlayerSceneTest.cs

Naming conventions

| Framework | GDScript file | C# file | Test method prefix/attribute | |-----------|---------------------|----------------------|------------------------------| | GUT | `test_*.gd` | N/A | `func test_*()` | | gdUnit4 | any name (`*_test.gd` when generated) | `*Test.cs` | `func test_*()` / `[TestCase]` |

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Running Tests

Both frameworks ship a CLI runner. **GUT:** `addons/gut/gut_cmdln.gd` invoked via `godot --headless --path . -s addons/gut/gut_cmdln.gd -gexit` (without `-gexit` the run never quits). **gdUnit4:** `addons/gdUnit4/runtest.sh -a res://tests` (wraps `bin/GdUnitCmdTool.gd`; under `--headless` it also needs `--ignoreHeadlessMode`), or the editor's GdUnit dock. CI: tag-triggered or PR-triggered GitHub Action that installs Godot, runs the suite, exits non-zero on failure.

> See [references/running-tests.md](references/running-tests.md) for full GUT and gdUnit4 CLI invocations + a copy-pasteable GitHub Actions workflow.

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Testing Patterns

Four common patterns: **scenes with nodes** (instantiate via `add_child` in `before_each`, free in `after_each`), **signal testing** (assert that emitting works and connect-then-emit fires), **mocking/doubling** (gdUnit4 `mock()` in GDScript; in C#, hand-rolled fakes via `@export` injection), **async** (await yields, signals, frames in tests).

> See [references/testing-patterns.md](references/testing-patterns.md) for full code on each pattern (GDScript + C# where applicable).

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Common Assertions

GUT assertions

| Assertion | Description | |----------------------------------------------|------------------------------------| | `assert_eq(actual, expected)` | Equality | | `assert_ne(actual, expected)` | Not equal | | `assert_true(value)` | Is truthy | | `assert_false(value)` | Is falsy | | `assert_null(value)` | Is null | | `assert_not_null(value)` | Is not null | | `assert_gt(actual, expected)` | Greater than | | `assert_lt(actual, expected)` | Less than | | `assert_gte(actual, expected)` | Greater than or equal | | `assert_lte(actual, expected)` | Less than or equal | | `assert_has(collection, item)` | Collection contains item | | `assert_does_not_have(collection, item)` | Collection does not contain item | | `assert_string_contains(str, sub)` | String contains substring | | `assert_almost_eq(actual, expected, margin)` | Float equality within margin | | `assert_signal_emitted(obj, signal_name)` | Signal was emitted | | `assert_signal_not_emitted(obj, signal_name)`| Signal was not emitted |

gdUnit4 assertions (GDScript + C#)

| GD