--- a/test/SbpOperators/volumeops/derivatives/first_derivative_test.jl	Mon Mar 02 13:51:56 2026 +0100
+++ b/test/SbpOperators/volumeops/derivatives/first_derivative_test.jl	Mon Mar 02 15:54:31 2026 +0100
@@ -16,6 +16,10 @@
         
         @test first_derivative(g₁, stencil_set) isa LazyTensor{Float64,1,1}
         @test first_derivative(g₂, stencil_set, 2) isa LazyTensor{Float64,2,2}
+        
+        @test first_derivative(g₁, stencil_set) == first_derivative(g₁, stencil_set, 1)
+        @test_throws DomainError(3, "Derivative direction must be 1.") first_derivative(g₁, stencil_set, 3)
+        @test_throws DomainError(3, "Derivative direction must be in 1:2.") first_derivative(g₂, stencil_set, 3)
 
         interior_stencil = CenteredStencil(-1,0,1)
         closure_stencils = [Stencil(-1,1, center=1)]