add directions basic tests

Author: andreapasquale94

test/Core/Core.jl

@@ -7,4 +7,5 @@ using SafeTestsets
     @safetestset "Transform: axes" begin include("transform_axes.jl") end
     @safetestset "Graph: points" begin include("points.jl") end
     @safetestset "Graph: frames" begin include("graph.jl") end
+    @safetestset "Graph: directions" begin include("directions.jl") end
 end;