--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/ext/sparse_arrays_test.jl	Tue Sep 10 21:59:10 2024 +0200
@@ -0,0 +1,34 @@
+using Test
+
+using Diffinitive
+using Diffinitive.Grids
+using Diffinitive.SbpOperators
+
+using SparseArrays
+using Tokens
+
+
+@testset "SparseArray" begin
+    g = equidistant_grid((0,0),(1,2), 20,30)
+    stencil_set = read_stencil_set(sbp_operators_path()*"standard_diagonal.toml"; order=4)
+
+
+    @testset let Δ = laplace(g, stencil_set), M = sparse(Δ)
+        @test ndims(M) == 2
+        @test size(M) == (20*30,20*30)
+
+        v = rand(size(g)...)
+
+        Mv = M*reshape(v,:)
+        @test Mv ≈ reshape(Δ*v,:)
+    end
+
+    @testset let dₙ = normal_derivative(g, stencil_set,CartesianBoundary{1,LowerBoundary}()), M = sparse(dₙ)
+        @test ndims(M) == 2
+        @test size(M) == (30,20*30)
+
+        v = rand(size(g)...)
+        Mv = M*reshape(v,:)
+        @test Mv ≈ reshape(dₙ*v,:)
+    end
+end