Move /src/test to /tests

tests/ui/parser/fn-defined-using-function.rs

@@ -0,0 +1,10 @@
+// Check what happens when `function` is used to define a function, instead of `fn`
+// edition:2021
+
+#![allow(dead_code)]
+
+function foo() {}
+//~^ ERROR expected one of `!` or `::`, found `foo`
+//~^^ HELP write `fn` instead of `function` to declare a function
+
+fn main() {}