Move /src/test to /tests

tests/ui/const-generics/const-fn-with-const-param.rs

@@ -0,0 +1,10 @@
+// Checks that `const fn` with const params can be used.
+// run-pass
+
+const fn const_u32_identity<const X: u32>() -> u32 {
+    X
+}
+
+fn main() {
+    assert_eq!(const_u32_identity::<18>(), 18);
+}