Add tests

src/test/ui/const-generics/const-param-in-trait-ungated.rs

@@ -0,0 +1,3 @@
+trait Trait<const T: ()> {} //~ ERROR const generics are unstable
+
+fn main() {}

src/test/ui/const-generics/const-param-in-trait-ungated.stderr

@@ -0,0 +1,12 @@
+error[E0658]: const generics are unstable
+  --> $DIR/const-param-in-trait-ungated.rs:1:19
+   |
+LL | trait Trait<const T: ()> {}
+   |                   ^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/44580
+   = help: add #![feature(const_generics)] to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/const-generics/const-param-in-trait.rs

@@ -0,0 +1,8 @@
+// run-pass
+
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+trait Trait<const T: ()> {}
+
+fn main() {}

src/test/ui/const-generics/const-param-in-trait.stderr

@@ -0,0 +1,6 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/const-param-in-trait.rs:3:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+