  We characterize two-weight norm inequalities for potential type integral
operators in terms of Sawyer-type testing conditions. Our result is stated in a
space of homogeneous type with no additional geometric assumptions, such as
group structure or non-empty annulus property, which appeared in earlier works
on the subject. One of the new ingredients in the proof is the use of a finite
collection of adjacent dyadic systems recently constructed by the author and T.
Hyt\"onen. We further extend the previous Euclidean characterization of
two-weight norm inequalities for fractional maximal functions into spaces of
homogeneous type.
