In circuit testing, diode function test and analog meters are not going
to be proof that the part is good although they will find bad parts
they will miss high resistance leakage in transistors.
Out of circuit tests with a good digital meter is also not positive
proof that the part is good but more likely than not if it shows good
then it proably is.
Whenever you are not sure check a new same type part (if possiable) and
see how it reads compaired to the suspected part.
Jeff