From a5c5b8fac882b230fd72e7a9255627a4ee5fa27a Mon Sep 17 00:00:00 2001
From: Yingbo Ma <mayingbo5@gmail.com>
Date: Wed, 19 Oct 2022 16:02:50 -0400
Subject: [PATCH] Add test

---
 test/reduction.jl | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/test/reduction.jl b/test/reduction.jl
index c0f22df73c..e534c7aa30 100644
--- a/test/reduction.jl
+++ b/test/reduction.jl
@@ -295,3 +295,10 @@ eqs = [x ~ 0
 ss = alias_elimination(sys)
 @test isempty(equations(ss))
 @test sort(observed(ss), by = string) == ([D(x), x, y] .~ 0)
+
+eqs = [D(D(x)) ~ -x]
+@named sys = ODESystem(eqs, t, [x], [])
+ss = alias_elimination(sys)
+@test length(equations(ss)) == length(states(ss)) == 1
+ss = structural_simplify(sys)
+@test length(equations(ss)) == length(states(ss)) == 2