From ad2a2227948415d0fbde0176e53716fe2ab8baf3 Mon Sep 17 00:00:00 2001
From: WooKyoung Noh <wookay.noh@gmail.com>
Date: Fri, 10 Feb 2017 05:13:48 +0900
Subject: [PATCH] Add a test throws an error by invalid subtyping in definition
 (#20523)

---
 test/subtype.jl | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/test/subtype.jl b/test/subtype.jl
index d8c6e6e53df4c9..cfe69037483cd7 100644
--- a/test/subtype.jl
+++ b/test/subtype.jl
@@ -911,3 +911,6 @@ ftwoparams(::TwoParams{<:Real,<:Real}) = 3
 @test TwoParams{Real,Complex}(3,0im) isa TwoParams{>:Int,<:Number}
 @test !(TwoParams(3.0,0im) isa TwoParams{>:Int,<:Number})
 @test !(TwoParams(3,'x') isa TwoParams{>:Int,<:Number})
+
+# Issue #20523
+@test_throws ErrorException immutable A20523 <: Base.AbstractSet; end