--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ts6.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,72 @@
+// { dg-do compile { target c++2a } }
+// { dg-additional-options "-fconcepts-ts" }
+
+template<typename T, int N, typename... Xs> concept bool C1 = true;
+
+template<template<typename> class X> concept bool C2 = true;
+
+template<typename... Ts> concept bool C3 = true;
+
+C1{A, B, ...C} struct S1 { };
+
+C2{T} void f();
+
+C2{...Ts} void g(); // { dg-error "cannot be introduced" }
+
+C3{...Ts} struct S2 { };
+C3{T, U, V} struct S3 { };
+C3{...Ts, U} struct S4 { }; // { dg-error "cannot deduce template parameters" }
+
+template<typename> struct X { };
+
+void driver1() {
+  S1<int, 0, char, bool, float> s1a;
+  S1<0, 0, char, bool, float> s1b; // { dg-error "type/value mismatch" }
+
+  f<X>();
+  f<int>(); // { dg-error "no matching function for call" }
+
+  S2<int> s2a;
+  S2<char, signed char, unsigned char> s2b;
+  S2<0> s2c; // { dg-error "type/value mismatch" }
+
+  S3<int, int, int> s3a;
+  S3<int, int> s3b; // { dg-error "wrong number of template arguments" }
+}
+
+template<typename... Args>
+struct all_same;
+
+template<typename T, typename U, typename... Args>
+struct all_same<T, U, Args...>
+{
+  static constexpr bool value = __is_same_as(T, U) && all_same<U, Args...>::value;
+};
+
+template<typename T>
+struct all_same<T>
+{
+  static constexpr bool value = true;
+};
+
+template<>
+struct all_same<>
+{
+  static constexpr bool value = true;
+};
+
+template<typename... Ts>
+concept AllSame = all_same<Ts...>::value;
+
+AllSame{...Ts} struct S5 { };
+AllSame{T, U} struct S6 { };
+
+void driver2()
+{
+  S5<int, int> s5a;
+  S5<int, int, int, int> s5b;
+  S5<int, int, int, char> s5c; // { dg-error "template constraint failure" }
+  S6<void, void> s6a;
+  S6<void, int> s6c; // { dg-error "template constraint failure" }
+  S6<void, void, void> s6b; // { dg-error "wrong number of template arguments" }
+}
\ No newline at end of file