Build & Test Troubleshooting FAQ

Purpose: Reference guide for diagnosing and resolving build failures, test failures, and other development environment issues.

When to use: When encountering unexpected build or test failures, especially those that seem environment-related rather than code-related.

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FAQ

Q1: NeoForge GameTest fails with "Illegal version number specified version (main)"

Symptoms:

File /path/to/neoforge-1.21.2/build/resources/main is not a valid mod file
Caused by: java.lang.IllegalArgumentException: Illegal version number specified version (main)

Cause: IDE (IntelliJ IDEA, Eclipse) generated

bin/

directories containing unprocessed resource files. The

neoforge.mods.toml

in

bin/main/META-INF/

has

version="${version}"

instead of the actual version number.

Solution:

1. Delete IDE-generated bin directories:

   rm -rf neoforge-1.21.2/bin common-1.21.2/bin
   

2. Or run the cleanAll task which now includes bin/ cleanup:

   ./gradlew cleanAll
   

Prevention:

• Configure IDE to use Gradle for builds instead of built-in compiler
• Add

  bin/

  to

  .gitignore

  (already done in this project)

Reference: Discovered 2026-01-25 during portal GameTest implementation.

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Q2: GameTest structure template not found or too small

Symptoms:

• Tests fail with "structure not found" errors
• Portal/structure tests fail because test area is too small

Cause:

• Fabric uses

  FabricGameTest.EMPTY_STRUCTURE

  constant (built-in)
• NeoForge requires explicit structure template files

Solution: For NeoForge, create a proper NBT structure file:

1. Create

   empty_test.nbt

   in

   common-{version}/src/main/resources/data/chronodawn/structure/

2. Reference it as

   "chronodawn:empty_test"

   in test configuration

Note: The structure must be large enough for the test content (e.g., 10x10x10 for portal frame tests).

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Q3: Gradle daemon conflicts during parallel builds

Symptoms:

• Build fails with lock file errors
• "Could not create service of type" errors
• Tests hang or fail intermittently

Solution:

./gradlew --stop
./gradlew cleanAll

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Q4: Test passes on Fabric but fails on NeoForge (or vice versa)

Checklist:

1. Mixin configurations: Check both loader-specific mixin JSON files
2. Structure templates: NeoForge needs explicit templates, Fabric has EMPTY_STRUCTURE
3. API differences: Some APIs behave differently between loaders
4. IDE artifacts: Run

   ./gradlew cleanAll

   to remove stale bin/ directories

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Q5: "session.lock" errors during GameTest

Symptoms:

Failed to lock the level ... session.lock

Cause: Previous test run left a lock file.

Solution: The

gameTestAll

task already handles this by cleaning stale world directories. If it persists:

rm -rf fabric-*/run/gametestworld
rm -rf neoforge-*/run/gametestworld

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Adding New FAQ Entries

When encountering a new build/test issue:

1. Document symptoms (exact error message)
2. Identify root cause
3. Document solution
4. Add prevention tips if applicable
5. Add reference date for tracking