first commit

backend/tests/test_rules.py

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+"""Tests for mutation rules."""
+
+from app.dataset.rules.python.null_pointer import NoneReferenceRule
+from app.dataset.rules.python.boundary_error import BoundaryErrorRule
+from app.dataset.rules.python.logic_operator import LogicOperatorRule
+from app.dataset.rules.registry import get_registry
+
+
+def test_python_none_reference():
+    src = """def process(data):
+    if data is not None:
+        x = data.upper()
+        return x
+"""
+    m = NoneReferenceRule().detect_and_mutate(src)
+    assert m is not None
+    assert m.defect_type == "null_pointer"
+    assert "if data is not None" not in m.mutated_source
+
+
+def test_python_boundary_error():
+    src = """def get(items, i):
+    if i < len(items):
+        return items[i]
+"""
+    m = BoundaryErrorRule().detect_and_mutate(src)
+    assert m is not None
+    assert "<=" in m.mutated_source
+
+
+def test_python_logic_operator():
+    src = """def ok(a, b):
+    return a and b
+"""
+    m = LogicOperatorRule().detect_and_mutate(src)
+    assert m is not None
+    assert " or " in m.mutated_source
+
+
+def test_registry_discovers_rules():
+    registry = get_registry()
+    assert "python" in registry.all_rules()
+    assert "java" in registry.all_rules()
+    assert "javascript" in registry.all_rules()