  Up to now, almost all discussion of supersymmetry at future colliders has
been concerned with particle searches. However, if candidates for
supersymmetric particles are found, there is much more that we will want to
know about them. Supersymmetry predicts quantitative relations among the
couplings and masses of supersymmetric particles. We discuss the prospects for
testing such relations at a future $e^+e^-$ linear collider, using measurements
that exploit the availability of polarized beams. Precision tests from chargino
production are investigated in two representative cases, and sfermion and
neutralino processes are also discussed.
