fix: use explain instead of msg as error explanation and add test

apps/emqx_schema_registry/src/emqx_schema_registry_serde.erl

@@ -74,7 +74,7 @@ handle_rule_function(schema_decode, [SchemaId, Data | MoreArgs]) ->
                     schema_id => SchemaId,
                     data => Data,
                     more_args => MoreArgs,
-                    msg =>
+                    explain =>
                         <<"The given data could not be decoded. Please check the input data and the schema.">>
                 }}
             )

apps/emqx_schema_registry/test/emqx_schema_registry_SUITE.erl

@@ -44,7 +44,8 @@ sparkplug_tests() ->
         t_sparkplug_decode,
         t_sparkplug_encode,
         t_sparkplug_decode_encode_with_message_name,
-        t_sparkplug_encode_float_to_uint64_key
+        t_sparkplug_encode_float_to_uint64_key,
+        t_decode_fail
     ].
 
 init_per_suite(Config) ->
@@ -532,6 +533,23 @@ t_encode(Config) ->
     end,
     ok.
 
+t_decode_fail(_Config) ->
+    SerdeName = my_serde,
+    SerdeType = protobuf,
+    ok = create_serde(SerdeType, SerdeName),
+    Payload = <<"ss">>,
+    ?assertThrow(
+        {schema_decode_error, #{
+            data := <<"ss">>,
+            error_type := decoding_failure,
+            explain := _,
+            more_args := [<<"Person">>],
+            schema_id := <<"my_serde">>
+        }},
+        emqx_rule_funcs:schema_decode(<<"my_serde">>, Payload, <<"Person">>)
+    ),
+    ok.
+
 t_decode(Config) ->
     SerdeType = ?config(serde_type, Config),
     SerdeName = my_serde,