  We analyze the surface tension exerted at the interface between an active
fluid and a solid boundary in terms of tangential forces. Focusing on active
systems known to possess an equation of state for the pressure, we show that
interfacial forces are of a more complex nature. Using a number of macroscopic
setups, we show that the surface tension is a combination of an
equation-of-state abiding part and of setup-dependent contributions. The latter
arise from generic setup-dependent steady currents which "dress" the
measurement of the "bare" surface tension. The former shares interesting
properties with its equilibrium counterpart, and can be used to generalize the
Young-Laplace law to active systems. We finally show how a suitably designed
probe can directly access this bare surface tensions, which can also be
computed using a generalized Virial formula.
