chore: add gametests

Author: scriptcoded

build.gradle

@@ -27,7 +27,30 @@ loom {
             sourceSet sourceSets.client
         }
     }
+}
+
+
+fabricApi {
+	configureTests {
+		createSourceSet = true
+		enableGameTests = true
+		enableClientGameTests = false
+		modId = "scl_tests"
+		eula = true
+	}
+}
+
+// `loom/runs` has to appear after the `fabricApi` block since it depends on
+// `sourceSets.gametest`, but `loom/splitEnvironmentSourceSets()` must be before.
+loom {
+	runs {
+		gameTestClient {
+			inherit client
 
+			configName = "GameTest Minecraft Client"
+			source = sourceSets.gametest
+		}
+	}
 }
 
 dependencies {

docs/testing.md

@@ -0,0 +1,55 @@
+# Testing
+
+This project uses the [Minecraft GameTest framework](https://minecraft.wiki/w/GameTest)
+along with [Fabric's GameTest integration](https://docs.fabricmc.net/develop/automatic-testing#writing-game-tests)
+for testing.
+
+File structure
+```
+src/
+  gametest/                                # Module for all things GameTest.
+    java/
+      io.nihlen.scriptschunkloaders/       # Package in which we put our tests.
+        ScriptsChunkLoadersGameTest.java   # We can have multiple test files. Also add to fabric.mod.json.
+    resources/
+      data.scl_tests/
+        structure/                         # Structures referenced by the tests live here.
+          basic.nbt
+          empty.nbt
+      fabric.mod.json                      # The GameTests are in their own mod which is defined here.
+  main/                                    # The ordinary mod files.
+```
+
+You can launch Minecraft with the GameTest mod loaded by running the "GameTest
+Minecraft Client" configuration.
+
+To design a new structure for a test, make sure to first define the structure in
+your test code:
+```java
+@GameTest(structure = "scl_tests:my_new_structure")
+public void my_new_test(TestContext context) {
+  // Your test goes here
+}
+```
+
+Then start the game. Open a world and run the command
+`/test create scl_tests:scripts_chunk_loaders_game_test_my_new_test`
+(autocomplete will help you).
+
+A test area will be generated in which your can design your test. To save the
+structure, right click the Test Block and click "Save Structure". Your structure
+will be saved in
+`run/saves/<your_save>/generated/scl_tests/structures/my_new_structure.nbt`.
+Move this into `src/gametest/resources/data/scl_tests/structure` to ensure it's
+commited into Git.
+
+## Hotswapping tests
+
+To hotswap tests, make sure to have your IDE configured to use the JetBrains
+Runtime and add `-XX:+AllowEnhancedClassRedefinition` to your VM Arguments for
+the "GameTest Minecraft Client" configuration. You can then start the game using
+the debugger and enjoy hotswapping of existing tests.
+
+You can read more about hotswapping in the [Fabric documentation](https://docs.fabricmc.net/develop/getting-started/launching-the-game#hotswapping-classes).
+
+