Fix error message for unimplemented domain/rangespace (#634)

Author: jishnub

src/Operators/Operator.jl

@@ -197,7 +197,7 @@ opissymmetric(::OperatorStyle, A) = false
 for f in [:domainspace, :rangespace]
     opf = Symbol(:op, f)
     @eval begin
-        $opf(::OperatorStyle, A) = error("Override domainspace for $(typeof(A))")
+        $opf(::OperatorStyle, A) = error("Override $($f) for $(typeof(A))")
         $opf(S::StyleConflict, A) = $opf(dominantstyle(S, $f, A), A)
     end
 end

test/runtests.jl

@@ -793,3 +793,10 @@ include("show.jl")
 
     @test @inferred(chebyshev_clenshaw(BigInt[1], 1)) == 1
 end
+
+@testset "Unimplemented functionality errors" begin
+    struct MyOperator{T} <: ApproxFunBase.Operator{T} end
+    X = MyOperator{Float64}();
+    @test_throws ErrorException("Override domainspace for $(typeof(X))") domainspace(X)
+    @test_throws ErrorException("Override rangespace for $(typeof(X))") rangespace(X)
+end