PLECK lesson 138 · suggested week 28, day 3
Read an error from the first useful cause
Objective. Distinguish parse, runtime and logic errors.
Godot Engine Standard desktop editor 4.7.2-stable, GDScript (Godot 4), Compatibility renderer. Headless Godot 4.7.2.stable.official.ed1daf0bf passed 106 assertions on the supplied scaffolds, including malformed JSON saves. Audio used the Dummy driver and a synthetic WAV, not a speaker. The visual editor, browser export, and signed-in submission were not tested. The desk still does not run a student's own upload.
About 55 minutes. The due date is chosen by a parent.
Pure functions, boundary cases, error reading and focused repair
Suggested pace: Recall and predict 5 min; Read instruction and scaffold 12 min; Build or design the assigned artifact 25 min; Run acceptance tests 8 min; Explain and checkpoint 5 min.
Materials: Godot Standard 4.7.2 desktop editor (GDScript, Compatibility renderer), Local course folder and prior checkpoint, No paid assets or public account required.
Comes after VGC-L137.
A parse error means the script could not be interpreted; a runtime error occurs while executing; a logic error runs but produces the wrong result. A misspelled variable may be caught before play, a missing $HUD/Score path may fail at runtime, and subtracting twice may silently produce the wrong score. Read the first relevant error and its file/line, then inspect the named context. Fixing a downstream symptom before the initial cause often wastes time. Use a duplicate lab for deliberate faults.
Worked example
A capacity function tested at below-minimum, middle and above-maximum inputs is easier to trust than one demonstrated only at a normal value. Scaffold C-TESTS — A tiny pure-function test harness Setup: Attach to Node TestLab. If using command line, create a separate SceneTree harness rather than running this Node script with --script. Run current TestLab scene in editor; assert reports a failed condition in Debugger. No external test framework or package is needed. ```gdscript extends Node func bounded_score(old_score: int, change: int) -> int: return clampi(old_score + change, 0, 999) func _ready() -> void: assert(bounded_score(10, 2) == 12) assert(bounded_score(0, -3) == 0) assert(bounded_score(998, 9) == 999) print("3 score checks passed") ```
A tiny pure-function test harness
GDScript (Godot 4, not Scratch, Python, JavaScript or C#). Scaffold C-TESTS. Copy starts from this text. The desk does not run it.
Scene and node setup
Attach to Node TestLab. If using command line, create a separate SceneTree harness rather than running this Node script with --script. Run current TestLab scene in editor; assert reports a failed condition in Debugger. No external test framework or package is needed.
extends Node
func bounded_score(old_score: int, change: int) -> int:
return clampi(old_score + change, 0, 999)
func _ready() -> void:
assert(bounded_score(10, 2) == 12)
assert(bounded_score(0, -3) == 0)
assert(bounded_score(998, 9) == 999)
print("3 score checks passed")
Checks to run in the editor
- All three assertions pass.
- Intentionally change expected 12 to 13 and observe a failure, then restore.
Native Godot 4.7.2.stable.official.ed1daf0bf headless compile and representative node-tree/runtime tests passed; see native-qa-results.json. Visual UI, audible output, exports and website submission still need separate checks.
Read an error from the first useful cause — evidence task
- 1. Create one safe example of each error category in a duplicate.
- 2. Record symptom, diagnostic clue and repair.
Deliverable. Three-category debugging report and clean lab.
Acceptance checks
- VGC-L138-T1. Each example is classified correctly.
- VGC-L138-T2. Restored lab has no remaining errors.
Understanding question. Is a game that runs without debugger errors necessarily correct?
Include a downloadable project ZIP with project.godot, .tscn, .gd and original asset files when code changes. A private, teacher-accessible download link to that ZIP is equivalent. Screenshots or a playthrough do not replace editable source.
If this is still shaky. Use C-TESTS and one ordinary plus two boundary cases. Keep a known-good snapshot before injecting faults. Start with the first assigned task and re-run its acceptance test before adding the remaining feature.
Optional extra. Add a property that should hold for many inputs and test a small finite range. Document one changed parameter, your prediction, and the observed effect; optional, not required for completion.
Turn in typed notes and a JPEG, PNG, or WebP screenshot. One https address is stored as text and is not opened, extracted, or run. An MP3, WAV, M4A, MP4, or WebM file up to 4 MB can show a demo. The demo does not replace editable source. Zip and code files are refused. If there is no private link, keep the project on the family computer and review the code in person.
- Your first 2D game
Free public tutorial; no account; external asset download is optional, not used by this course.
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