There is no default password. Common passwords are "password", the user name
itself (in this case tester), and no password. The tester account is one
hint that it is not too serious an account. Also try the administrator
account. Failing that, you can find password reset programs on line, or you
can reinstall Windows.
Whoever you bought the computer from should have either been the owner, in
which case, they can tell you the password, or a reseller, who, in making
sure the system actually worked, should have noticed that it required a
password, and gotten it.
Also, if your used computer did not come with a Windows CD, then you may not
in fact own a licensed copy of Windows. If it is a name brand computer, with
a manufacturer serial number on it, you can at least ascertain if it came
with an OEM copy, which in many cases means it shipped with Windows
preinstalled. In that case, no worries.
