Start FieldTypeTest.
Dry up by extracting getBytes call.
Pass field name instead of Binding to FieldType.

Also rename getTupleBytes -> getBytes.
Test FieldType::getBytes.
Rename addToTuple -> add.

It's not actually a tuple, in the end.
Prove badly sized byte arrays fail loudly.

Don't bother wrapping the generated exception either: BufferUnderflowException is fine.