insert a BLOB via a sql script?

For testing, you can insert literal hex bytes or use the RAWTOHEX(string) function, as shown below.

create table a(id integer, item blob);
insert into a values(1,'54455354');
insert into a values(2, RAWTOHEX('Test'));
select UTF8TOSTRING(item) from a;
TEST
Test

Addendum: For loading BLOB fields from a file, FILE_READ(fileNameString) may be a useful alternative.

insert into a values(3, FILE_READ('file.dat'));