Add test for kronecker operator multiplication (#294)

Author: jishnub

test/MultivariateTest.jl

@@ -276,11 +276,11 @@ include("testutils.jl")
         testbandedblockbandedoperator(Dx)
         f = Fun((x,y) -> sin(x) * cos(y), d)
         fx = Fun((x,y) -> cos(x) * cos(y), d)
-        @test (Dx*f)(0.2,0.3) ≈ fx(0.2,0.3)
+        @test (Dx*f)(0.2,0.3) ≈ ((Derivative() ⊗ I) * f)(0.2,0.3) ≈ fx(0.2,0.3)
         Dy = Derivative(d, [0,1])
         testbandedblockbandedoperator(Dy)
         fy = Fun((x,y) -> -sin(x) * sin(y), d)
-        @test (Dy*f)(0.2,0.3) ≈ fy(0.2,0.3)
+        @test (Dy*f)(0.2,0.3) ≈ ((I ⊗ Derivative()) * f)(0.2,0.3) ≈ fy(0.2,0.3)
         L = Dx + Dy
         testbandedblockbandedoperator(L)
         @test (L*f)(0.2,0.3) ≈ (fx(0.2,0.3)+fy(0.2,0.3))