It would be good to do a run of 10.2 tests against 10.3 to see if there are any obvious incompatibilities
10.2 client Stream.java test fails when run against 10.3 with Java exception: 'Reversed byte-order mark: sun.io.MalformedInputException'.
Resolve difference of type compatibility between Embedded and NetworkServer/NetworkDriver
Client connections should not fail if permission is not granted to read derby.client.traceLevel and derby.client.traceDirectory
10.2 derbynet/testProperties.java test hangs when run against 10.3
10.2 client procedure.java test fails when run against 10.3 server with ERROR X0X03: Invalid transaction state - held cursor requires same isolation level
10.2 client blobclob4blob test run against 10.3 server fails for many tests with SQLSTATE(XJ073): The data in this BLOB or CLOB is no longer available.