Why should I test the code, if it works all the same?

I'm wild about it:

Almost pseudo code:

databaseAdapter.open(UID,PWD);
databaseAdapter.execute("select 2 from dual");
databaseAdapter.close();
databaseAdapter.open(UID,PWD);
databaseAdapter.execute("select 2 from dual");
databaseAdapter.close();

It falls on the second select.