Add CI workflow and reusable test-harness foundation

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_helpers.gd

@@ -0,0 +1,47 @@
+class_name TestHelpers
+extends RefCounted
+## Shared primitives for the headless test suite so each test stops re-implementing them: a seeded
+## RNG for determinism, float/vector approximate comparisons, and a small pass/fail tally whose
+## report() doubles as the process exit code. Use the tally directly, or the static helpers alone.
+
+var _pass: int = 0
+var _fail: int = 0
+
+
+# Determinism is the precondition for repeatable AI/physics tests: seed the RNG here instead of the
+# global randf()/randi() so a test replays identically every run.
+static func make_rng(seed_value: int) -> RandomNumberGenerator:
+	var rng := RandomNumberGenerator.new()
+	rng.seed = seed_value
+	return rng
+
+
+static func approx(a: float, b: float, eps: float = 0.0001) -> bool:
+	return absf(a - b) <= eps
+
+
+static func vec_approx(a: Vector3, b: Vector3, eps: float = 0.0001) -> bool:
+	return a.distance_to(b) <= eps
+
+
+func ok(cond: bool, msg: String) -> void:
+	if cond:
+		_pass += 1
+		print("  PASS: ", msg)
+	else:
+		_fail += 1
+		print("  FAIL: ", msg)
+
+
+func passed() -> int:
+	return _pass
+
+
+func failed() -> int:
+	return _fail
+
+
+## Prints the tally and returns the process exit code (0 = everything passed).
+func report() -> int:
+	print("Results: %d passed, %d failed" % [_pass, _fail])
+	return 1 if _fail > 0 else 0