fix: include literal values in equivalence checks

multiplex/checks/syntactic_equivalence.py

@@ -4,35 +4,37 @@
 import tree_sitter_java as ts_java
 
 
-def _get_clean_tree(source_code, parser):
-    tree = parser.parse(source_code.text, encoding="utf-8")
-    root_node = tree.root_node
+def _get_clean_tree(root_node) -> str:
+    """Serialize a parse tree to a string for comparison.
 
-    def traverse(node):
+    Comments and whitespace are ignored. 
+    Leaf tokens include their source text to include values in comparison.
+    """
+
+    def traverse(node) -> str:
         if node.type in ("comment", "line_comment", "block_comment", "whitespace"):
             return ""
         if node.child_count == 0:
-            return node.type
-        return node.type + "(" + "".join([traverse(child) for child in node.children]) + ")"
+            return node.type + "-" + node.text.decode("utf-8")
+        return node.type + "(" + "".join(traverse(child) for child in node.children) + ")"
 
     return traverse(root_node)
 
 
-def _tree_is_equivalent(original_root_node, mutant_root_node, parser):
+def _tree_is_equivalent(original_root_node, mutant_root_node):
     """Check tree for equivalence."""
-    mutant = _get_clean_tree(mutant_root_node, parser)
-    original = _get_clean_tree(original_root_node, parser)
+    mutant = _get_clean_tree(mutant_root_node)
+    original = _get_clean_tree(original_root_node)
 
     seq_match = SequenceMatcher(None, original, mutant)
     ratio = seq_match.ratio()
     print("Syntactic Equivalence Ratio:", ratio)
 
-    if mutant == original:
-        return True
-    return False
+    return mutant == original
 
 
 def _read_file(fn):
+    """Read file"""
     src = ""
     with open(fn, "r", encoding="utf-8") as reader:
         src = reader.read()
@@ -45,4 +47,4 @@ def check_mutant_equivalent(mutant_filename, original_filename) -> bool:
     parser = Parser(language)
     mutant_tree = parser.parse(_read_file(mutant_filename), encoding="utf-8")
     original_tree = parser.parse(_read_file(original_filename), encoding="utf-8")
-    return _tree_is_equivalent(original_tree.root_node, mutant_tree.root_node, parser)
+    return _tree_is_equivalent(original_tree.root_node, mutant_tree.root_node)

tests/checks/test_syntactic_equivalence.py

@@ -25,3 +25,41 @@ def test_check_mutant_equivalent_is_equivalent(equivalent_mutant_path, original_
 def test_check_mutant_equivalent_not_equivalent(killed_mutant_path, original_method_path):
     """Check mutant identified as not equivalent."""
     assert not check_mutant_equivalent(killed_mutant_path, original_method_path)
+
+
+def _write(tmp_path, name, code):
+    p = tmp_path / name
+    p.write_text(code)
+    return p
+
+
+def test_string_literal_change_is_not_equivalent(tmp_path):
+    """A changed string literal (same AST shape) must not be equivalent."""
+    original = _write(tmp_path, "o.java", 'String f() { return "negative"; }')
+    mutant = _write(tmp_path, "m.java", 'String f() { return "positive"; }')
+    assert not check_mutant_equivalent(mutant, original)
+
+
+def test_numeric_literal_change_is_not_equivalent(tmp_path):
+    original = _write(tmp_path, "o.java", "int f() { return 1; }")
+    mutant = _write(tmp_path, "m.java", "int f() { return 2; }")
+    assert not check_mutant_equivalent(mutant, original)
+
+
+def test_identifier_change_is_not_equivalent(tmp_path):
+    original = _write(tmp_path, "o.java", "int f(int a, int b) { return a; }")
+    mutant = _write(tmp_path, "m.java", "int f(int a, int b) { return b; }")
+    assert not check_mutant_equivalent(mutant, original)
+
+
+def test_comment_only_change_is_equivalent(tmp_path):
+    """Differences only in comments/whitespace remain equivalent."""
+    original = _write(tmp_path, "o.java", "int f() { return 1; }")
+    mutant = _write(tmp_path, "m.java", "int f() {\n    // added comment\n    return 1;\n}")
+    assert check_mutant_equivalent(mutant, original)
+
+
+def test_identical_source_is_equivalent(tmp_path):
+    original = _write(tmp_path, "o.java", "int f() { return 1; }")
+    mutant = _write(tmp_path, "m.java", "int f() { return 1; }")
+    assert check_mutant_equivalent(mutant, original)