Deny having src/test exisiting in tidy

src/tools/tidy/src/lib.rs

@@ -64,6 +64,7 @@ pub mod pal;
 pub mod primitive_docs;
 pub mod style;
 pub mod target_specific_tests;
+pub mod tests_placement;
 pub mod ui_tests;
 pub mod unit_tests;
 pub mod unstable_book;

src/tools/tidy/src/main.rs

@@ -76,6 +76,7 @@ fn main() {
         check!(extdeps, &root_path);
 
         // Checks over tests.
+        check!(tests_placement, &root_path);
         check!(debug_artifacts, &tests_path);
         check!(ui_tests, &tests_path);
         check!(mir_opt_tests, &tests_path, bless);

src/tools/tidy/src/tests_placement.rs

@@ -0,0 +1,15 @@
+use std::path::Path;
+
+const FORBIDDEN_PATH: &str = "src/test";
+const ALLOWED_PATH: &str = "tests";
+
+pub fn check(root_path: impl AsRef<Path>, bad: &mut bool) {
+    if root_path.as_ref().join(FORBIDDEN_PATH).exists() {
+        tidy_error!(
+            bad,
+            "Tests have been moved, please move them from {} to {}",
+            root_path.as_ref().join(FORBIDDEN_PATH).display(),
+            root_path.as_ref().join(ALLOWED_PATH).display()
+        )
+    }
+}