fans: fix negation, add testset

Author: benlorenz

src/PolyhedralGeometry/PolyhedralFan/standard_constructions.jl

@@ -433,7 +433,7 @@ end
 ###############################################################################
 
 function -(Sigma::PolyhedralFan)
-  SigmaRays, SigmaLineality = first(rays_modulo_lineality(Sigma))
+  SigmaRays, SigmaLineality = rays_modulo_lineality(Sigma)
   SigmaIncidence = maximal_cones(IncidenceMatrix, Sigma)
   return polyhedral_fan(
     coefficient_field(Sigma), SigmaIncidence, -SigmaRays, SigmaLineality

test/PolyhedralGeometry/polyhedral_fan.jl

@@ -218,7 +218,9 @@ end
   sff1 = star_subdivision(ff, w1)
   @test number_of_maximal_cones(sff0) == 2
   @test number_of_maximal_cones(sff1) == 3
+end
 
+@testset "Operations" begin
   f = normal_fan(cube(2))
   fMinus = -f
   @test n_rays(fMinus) == n_rays(f)