diff --git a/src/Architecture/DenseLayerOp.jl b/src/Architecture/DenseLayerOp.jl
index bd613ae..40dd1fe 100644
--- a/src/Architecture/DenseLayerOp.jl
+++ b/src/Architecture/DenseLayerOp.jl
@@ -33,7 +33,8 @@ function _isconsistent(weights, bias)
     return size(weights, 1) == length(bias)
 end
 
-(l::DenseLayerOp)(x) = l.activation.(l.weights * x .+ l.bias)
+# application to a vector
+(L::DenseLayerOp)(x) = L.activation.(L.weights * x .+ L.bias)
 
 Base.length(L::DenseLayerOp) = length(L.bias)
 
diff --git a/test/Architecture/AbstractLayerOp.jl b/test/Architecture/AbstractLayerOp.jl
new file mode 100644
index 0000000..c42c2e9
--- /dev/null
+++ b/test/Architecture/AbstractLayerOp.jl
@@ -0,0 +1,5 @@
+# AbstractLayerOp implementation
+struct TestLayerOp <: AbstractLayerOp end
+L = TestLayerOp()
+dim_in(L)
+dim_out(L)
diff --git a/test/Architecture/DenseLayerOp.jl b/test/Architecture/DenseLayerOp.jl
index 2655a14..46989d9 100644
--- a/test/Architecture/DenseLayerOp.jl
+++ b/test/Architecture/DenseLayerOp.jl
@@ -1,11 +1,5 @@
 using ReachabilityBase.Subtypes: subtypes
 
-# AbstractLayerOp implementation
-struct TestLayerOp <: AbstractLayerOp end
-L = TestLayerOp()
-dim_in(L)
-dim_out(L)
-
 # 2D input vector and 2x3 layer
 x = [1.0, 1]
 W = hcat([1 0.5; -0.5 0.5; -1 -0.5])
diff --git a/test/runtests.jl b/test/runtests.jl
index 748c6f7..5a06c1d 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -7,6 +7,9 @@ import Flux, MAT, ONNX, YAML
 struct TestActivation <: ActivationFunction end
 
 @testset "Architecture" begin
+    @testset "AbstractLayerOp" begin
+        include("Architecture/AbstractLayerOp.jl")
+    end
     @testset "DenseLayerOp" begin
         include("Architecture/DenseLayerOp.jl")
     end