TST: improve test_mann_whitney_u_R
TST: improve test_mann_whitney_u_R

spacetelescope/asv,airspeed-velocity/asv,spacetelescope/asv,airspeed-velocity/asv,spacetelescope/asv,airspeed-velocity/asv,airspeed-velocity/asv,spacetelescope/asv