test not-implemented conversion

Author: dlfivefifty

src/classical/jacobi.jl

@@ -316,8 +316,7 @@ function _jacobi_convert_b(a, b, k, T) # Jacobi(a, b+k) \ Jacobi(a, b)
     end
 end
 
-isapproxinteger(::Integer) = true
-isapproxinteger(x) = isinteger(x) || isapprox(x,round(Int,x))  || isapprox(x+1,round(Int,x+1))
+isapproxinteger(x) = isinteger(x) || isapprox(x,round(Int,x)) || isapprox(x+1,round(Int,x+1))
 
 
 function \(A::Jacobi, B::Jacobi)

test/test_jacobi.jl

@@ -533,4 +533,8 @@ import ClassicalOrthogonalPolynomials: recurrencecoefficients, basis, MulQuasiMa
         @test (P² \ diff(P¹,1))[1:10,1:10] ≈ (P² \ diff(P¹))[1:10,1:10]
         @test (P³ \ diff(P¹,2))[1:10,1:10] ≈ (P³ \ diff(diff(P¹)))[1:10,1:10]
     end
+
+    @testset "conversion not implemented" begin 
+        @test_throws ArgumentError Jacobi(0,0) \ Jacobi(1.1,2.1)
+    end
 end