test(merkle): Add comprehensive unit tests for MerkleTree

Implement various test cases for MerkleTree initialization,
authentication path generation, and decommitment verification.
Include edge cases and a large tree test for thorough coverage.

tests/test_merkle.py

@@ -0,0 +1,74 @@
+import unittest
+from hashlib import sha256
+import sys
+
+sys.path.append("../src")
+sys.path.append("src")
+from merkle import MerkleTree, verify_decommitment
+
+class TestMerkleTree(unittest.TestCase):
+
+    def test_init_with_valid_data(self):
+        data = [1, 2, 3, 4]
+        tree = MerkleTree(data)
+        self.assertEqual(len(tree.data), 4)
+        self.assertEqual(tree.height, 2)
+
+    def test_init_with_non_power_of_two_data(self):
+        data = [1, 2, 3]
+        tree = MerkleTree(data)
+        self.assertEqual(len(tree.data), 4)
+        self.assertEqual(tree.height, 2)
+        self.assertEqual(tree.data[-1], 0)  # Check padding
+
+    def test_init_with_empty_list(self):
+        with self.assertRaises(AssertionError):
+            MerkleTree([])
+
+    def test_get_authentication_path(self):
+        data = [1, 2, 3, 4]
+        tree = MerkleTree(data)
+        path = tree.get_authentication_path(0)
+        self.assertEqual(len(path), 2)
+
+    def test_get_authentication_path_out_of_range(self):
+        data = [1, 2, 3, 4]
+        tree = MerkleTree(data)
+        with self.assertRaises(AssertionError):
+            tree.get_authentication_path(4)
+
+    def test_verify_decommitment(self):
+        data = [1, 2, 3, 4]
+        tree = MerkleTree(data)
+        leaf_id = 2
+        leaf_data = data[leaf_id]
+        path = tree.get_authentication_path(leaf_id)
+        self.assertTrue(verify_decommitment(leaf_id, leaf_data, path, tree.root))
+
+    def test_verify_decommitment_with_wrong_leaf_data(self):
+        data = [1, 2, 3, 4]
+        tree = MerkleTree(data)
+        leaf_id = 2
+        wrong_leaf_data = 5
+        path = tree.get_authentication_path(leaf_id)
+        self.assertFalse(verify_decommitment(leaf_id, wrong_leaf_data, path, tree.root))
+
+    def test_verify_decommitment_with_wrong_path(self):
+        data = [1, 2, 3, 4]
+        tree = MerkleTree(data)
+        leaf_id = 2
+        leaf_data = data[leaf_id]
+        path = tree.get_authentication_path(leaf_id)
+        wrong_path = [sha256(b'wrong').hexdigest() for _ in path]
+        self.assertFalse(verify_decommitment(leaf_id, leaf_data, wrong_path, tree.root))
+
+    def test_large_tree(self):
+        data = list(range(1024))
+        tree = MerkleTree(data)
+        self.assertEqual(tree.height, 10)
+        for i in range(1024):
+            path = tree.get_authentication_path(i)
+            self.assertTrue(verify_decommitment(i, data[i], path, tree.root))
+
+if __name__ == '__main__':
+    unittest.main()