Test our implementation against Cryptography module's

tests/test_chacha.py

@@ -7,6 +7,7 @@ from randquik import cha
 
 
 def test_cipherstreams_fullblocks():
+    """Requests in multiple of ChaCha20 block size 64 bytes"""
     key = token_bytes(32)
     nonce = token_bytes(16)
     c0 = Cipher(ChaCha20(key, nonce), None, None).encryptor()
@@ -21,6 +22,7 @@ def test_cipherstreams_fullblocks():
 
 
 def test_cipherstreams_partial_updates():
+    """Odd-sized requests that retain leftover buffers"""
     key = token_bytes(32)
     nonce = token_bytes(16)
     c0 = Cipher(ChaCha20(key, nonce), None, None).encryptor()
@@ -32,3 +34,17 @@ def test_cipherstreams_partial_updates():
         ct1 = c1(bytearray(N))
         assert len(ct0) == len(ct1)
         assert ct0.hex() == ct1.hex()
+
+
+def test_cipherstreams_32leftover():
+    """Test the special case where the second response comes entirely from the leftover buffer"""
+    key = token_bytes(32)
+    nonce = token_bytes(16)
+    c0 = Cipher(ChaCha20(key, nonce), None, None).encryptor()
+    c1 = cha.Cha(key, nonce)
+
+    for N in [512 - 32, 32]:
+        ct0 = c0.update(bytes(N))
+        ct1 = c1(bytearray(N))
+        assert len(ct0) == len(ct1)
+        assert ct0.hex() == ct1.hex()