fix: Add validation for size parameter in ABConfig

tests/test_ab.py

@@ -1,5 +1,7 @@
 import random
+
 import pytest
+
 from reasoning_gym.algorithmic.ab import ABConfig, ABDataset, compute_steps, generate_program
 
 
@@ -28,17 +30,17 @@ def test_ab_program_generation():
     """Test program generation and computation"""
     rng = random.Random(42)
     program = generate_program(5, rng)
-    
+
     # Test program format
     assert len(program) == 5
     assert all(token in ["A#", "#A", "B#", "#B"] for token in program)
-    
+
     # Test computation
     steps, non_halting = compute_steps(program)
     assert isinstance(steps, list)
     assert isinstance(non_halting, bool)
     assert len(steps) > 0
-    
+
     # Test each step follows valid transformation rules
     for step in steps:
         assert all(token in ["A#", "#A", "B#", "#B"] for token in step)
@@ -48,15 +50,15 @@ def test_ab_scoring():
     """Test scoring functionality"""
     config = ABConfig(seed=42, size=10, length=5)
     dataset = ABDataset(config)
-    
+
     for item in dataset:
         # Test correct answer
         assert dataset.score_answer(answer=item["answer"], entry=item) == 1.0
-        
+
         # Test wrong answer
         wrong_answer = "A# B#" if item["answer"] != "A# B#" else "B# A#"
         assert dataset.score_answer(answer=wrong_answer, entry=item) == 0.01
-        
+
         # Test None answer
         assert dataset.score_answer(answer=None, entry=item) == 0.0
 
@@ -65,14 +67,14 @@ def test_ab_iteration():
     """Test dataset iteration behavior"""
     config = ABConfig(size=5, seed=42)
     dataset = ABDataset(config)
-    
+
     # Test length
     assert len(dataset) == config.size
-    
+
     # Test iteration
     items = list(dataset)
     assert len(items) == config.size
-    
+
     # Test multiple iterations yield same results
     items2 = list(dataset)
     assert items == items2
@@ -88,11 +90,11 @@ def test_ab_item_structure():
         assert "question" in item
         assert "answer" in item
         assert "metadata" in item
-        
+
         # Test question format
         assert "A::B is a system" in item["question"]
         assert "Return the final state" in item["question"]
-        
+
         # Test answer format
         answer_tokens = item["answer"].split()
         assert all(token in ["A#", "#A", "B#", "#B"] for token in answer_tokens)