fix 'an_element' fallback for unbounded sets

Author: schillic

src/Interfaces/LazySet.jl

@@ -641,7 +641,11 @@ end
 function _an_element_lazySet(X::LazySet)
     N = eltype(X)
     e₁ = SingleEntryVector(1, dim(X), one(N))
-    return σ(e₁, X)
+    v = σ(e₁, X)
+    if any(isinf, v)
+        throw(ArgumentError("this implementation assumes a bounded set"))
+    end
+    return v
 end
 
 # hook into random API

test/Interfaces/LazySet.jl

@@ -0,0 +1,5 @@
+for N in [Float64, Float32, Rational{Int}]
+    # an_element default implementation
+    U = Universe{N}(2)
+    @test_throws ArgumentError LazySets._an_element_lazySet(U)
+end

test/runtests.jl

@@ -251,6 +251,9 @@ if test_suite_basic
     @testset "LazySets.CompactSet" begin
         include("Interfaces/CompactSet.jl")
     end
+    @testset "LazySets.LazySet" begin
+        include("Interfaces/LazySet.jl")
+    end
 
     # =======================
     # Concrete set operations