Test message parsing with Message'Size

ref #525

tests/data/fixtures/pyrflx.py

@@ -23,6 +23,7 @@ def fixture_pyrflx() -> pyrflx.PyRFLX:
             f"{SPEC_DIR}/null_message.rflx",
             f"{SPEC_DIR}/tlv.rflx",
             f"{SPEC_DIR}/tlv_with_checksum.rflx",
+            f"{SPEC_DIR}/message_size.rflx",
         ],
         skip_model_verification=True,
     )
@@ -179,3 +180,13 @@ def fixture_array_message_package(pyrflx_: pyrflx.PyRFLX) -> pyrflx.Package:
 @pytest.fixture(name="array_message_value")
 def fixture_array_message_value(array_message_package: pyrflx.Package) -> pyrflx.MessageValue:
     return array_message_package["Message"]
+
+
+@pytest.fixture(name="message_size_package", scope="session")
+def fixture_message_size_package(pyrflx_: pyrflx.PyRFLX) -> pyrflx.Package:
+    return pyrflx_["Message_Size"]
+
+
+@pytest.fixture(name="message_size")
+def fixture_message_size(message_size_package: pyrflx.Package) -> pyrflx.MessageValue:
+    return message_size_package["Msg"]

tests/data/specs/message_size.rflx

@@ -0,0 +1,15 @@
+package Message_Size is
+
+   type T is mod 2**8;
+
+   type Msg is
+      message
+         A : T
+            then B
+               with Size => A * 8;
+         B : Opaque
+            then null
+               if Message'Size = (A + 1) * 8;
+      end message;
+
+end Message_Size;

tests/unit/pyrflx_test.py

@@ -62,6 +62,7 @@ def test_pyrflx_iterator(pyrflx_: PyRFLX) -> None:
         "Ethernet",
         "ICMP",
         "IPv4",
+        "Message_Size",
         "TLS_Alert",
         "TLS_Record",
         "TLV",
@@ -1156,3 +1157,10 @@ def test_unaligned_field_serialization(data: bytes, f1: int, f2: int, f3: int) -
     assert msg.get("F2") == f2
     assert msg.get("F3") == f3
     assert data == msg.bytestring
+
+
+def test_message_size(message_size: MessageValue) -> None:
+    message_size.parse(b"\x02\x01\x02")
+    assert message_size.valid_message
+    assert message_size.get("A") == 2
+    assert message_size.get("B") == b"\x01\x02"