[GEMINI] Add unit tests for concrete BaseDecoder subclasses and DecodingRegistry

tests/test_decoding.py

@@ -133,5 +133,31 @@ def test_try_decode_metadata_rot13_unique_only():
     assert "rot13" not in res_duplicate
 # }}}
 
+# {{{ test_decoder_subclasses_and_registry
+def test_decoder_subclasses_and_registry():
+    """
+    Verifies that DecodingRegistry successfully registers concrete decoders and
+    that individual BaseDecoder subclasses correctly decode matching strings.
+    """
+    from ctf.decoding import DecodingRegistry, Base64Decoder, HexDecoder, Rot13Decoder
+    
+    registry = DecodingRegistry.get_default_registry()
+    assert len(registry.decoders) >= 7
+    
+    # Assert Base64Decoder behaves correctly
+    b64_dec = Base64Decoder()
+    assert b64_dec.name == "base64"
+    assert b64_dec.is_applicable("ZmxhZ3tiNjRfbWV0YWRhdGF9")
+    assert not b64_dec.is_applicable("A")
+    assert b64_dec.attempt_single("ZmxhZ3tiNjRfbWV0YWRhdGF9") == "flag{b64_metadata}"
+    
+    # Assert Rot13Decoder validates correctly
+    rot_dec = Rot13Decoder()
+    assert rot_dec.name == "rot13"
+    assert rot_dec.attempt_single("synt{ebg13}") == "flag{rot13}"
+    assert rot_dec.attempt_single("abezny grkg") is None  # Fails validate check
+# }}}
+
+