added tests to ensure no nesting is happening

Author: vpuri3

test/basic.jl

@@ -221,6 +221,14 @@ end
     v=rand(N,K); @test ldiv!(v, op, u) ≈ (A * B * C) \ u
     v=copy(u);   @test ldiv!(op, u)    ≈ (A * B * C) \ v
 
+    # ensure composedoperators don't nest
+    A = MatrixOperator(rand(N, N))
+    L = A * (A * A) * A
+    @test L isa ComposedOperator
+    for op in L.ops
+        @test !isa(op, ComposedOperator)
+    end
+
     # Test caching of composed operator when inner ops do not support Base.:*
     # ComposedOperator caching was modified in PR # 174
     inner_op = qr(MatrixOperator(rand(N, N)))

test/scalar.jl

@@ -1,6 +1,14 @@
 #
-using SciMLOperators, LinearAlgebra
-using Random
+using SciMLOperators
+using SciMLOperators: AbstractSciMLScalarOperator,
+                      ComposedScalarOperator,
+                      AddedScalarOperator,
+                      InvertedScalarOperator,
+                      IdentityOperator,
+                      AddedOperator,
+                      ScaledOperator
+
+using LinearAlgebra, Random
 
 Random.seed!(0)
 N = 8
@@ -38,31 +46,31 @@ K = 12
 
     # Test that ScalarOperator's remain AbstractSciMLScalarOperator's under common ops
     β = α + α
-    @test β isa SciMLOperators.AddedScalarOperator
+    @test β isa AddedScalarOperator
     @test β * u ≈ x * u + x * u
     @inferred convert(Float32, β)
     @test convert(Number, β) ≈ x + x
 
     β = α * α
-    @test β isa SciMLOperators.ComposedScalarOperator
+    @test β isa ComposedScalarOperator
     @test β * u ≈ x * x * u
     @inferred convert(Float32, β)
     @test convert(Number, β) ≈ x * x
 
     β = inv(α)
-    @test β isa SciMLOperators.InvertedScalarOperator
+    @test β isa InvertedScalarOperator
     @test β * u ≈ 1 / x * u
     @inferred convert(Float32, β)
     @test convert(Number, β) ≈ 1 / x
 
     β = α * inv(α)
-    @test β isa SciMLOperators.ComposedScalarOperator
+    @test β isa ComposedScalarOperator
     @test β * u ≈ u
     @inferred convert(Float32, β)
     @test convert(Number, β) ≈ true
 
     β = α / α
-    @test β isa SciMLOperators.ComposedScalarOperator
+    @test β isa ComposedScalarOperator
     @test β * u ≈ u
     @inferred convert(Float32, β)
     @test convert(Number, β) ≈ true
@@ -77,6 +85,14 @@ K = 12
         @test (α / op) * u ≈ (op \ α) * u ≈ α * (op \ u)
         @test (op / α) * u ≈ (α \ op) * u ≈ 1/α * op * u
     end
+
+    # ensure composedscalaroperators doesn't nest
+    α = ScalarOperator(rand())
+    L = α * (α * α) * α
+    @test L isa ComposedScalarOperator
+    for op in L.ops
+        @test !isa(op, ComposedScalarOperator)
+    end
 end
 
 @testset "ScalarOperator update test" begin