diff --git a/src/librustc_incremental/persist/fs.rs b/src/librustc_incremental/persist/fs.rs
index 0ab67af613b..511175de5d8 100644
--- a/src/librustc_incremental/persist/fs.rs
+++ b/src/librustc_incremental/persist/fs.rs
@@ -117,6 +117,9 @@ use std::time::{UNIX_EPOCH, SystemTime, Duration};
 
 use rand::{RngCore, thread_rng};
 
+#[cfg(test)]
+mod tests;
+
 const LOCK_FILE_EXT: &str = ".lock";
 const DEP_GRAPH_FILENAME: &str = "dep-graph.bin";
 const WORK_PRODUCTS_FILENAME: &str = "work-products.bin";
@@ -894,67 +897,3 @@ fn safe_remove_file(p: &Path) -> io::Result<()> {
         Ok(())
     }
 }
-
-#[test]
-fn test_all_except_most_recent() {
-    assert_eq!(all_except_most_recent(
-        vec![
-            (UNIX_EPOCH + Duration::new(4, 0), PathBuf::from("4"), None),
-            (UNIX_EPOCH + Duration::new(1, 0), PathBuf::from("1"), None),
-            (UNIX_EPOCH + Duration::new(5, 0), PathBuf::from("5"), None),
-            (UNIX_EPOCH + Duration::new(3, 0), PathBuf::from("3"), None),
-            (UNIX_EPOCH + Duration::new(2, 0), PathBuf::from("2"), None),
-        ]).keys().cloned().collect::<FxHashSet<PathBuf>>(),
-        vec![
-            PathBuf::from("1"),
-            PathBuf::from("2"),
-            PathBuf::from("3"),
-            PathBuf::from("4"),
-        ].into_iter().collect::<FxHashSet<PathBuf>>()
-    );
-
-    assert_eq!(all_except_most_recent(
-        vec![
-        ]).keys().cloned().collect::<FxHashSet<PathBuf>>(),
-        FxHashSet::default()
-    );
-}
-
-#[test]
-fn test_timestamp_serialization() {
-    for i in 0 .. 1_000u64 {
-        let time = UNIX_EPOCH + Duration::new(i * 1_434_578, (i as u32) * 239_000);
-        let s = timestamp_to_string(time);
-        assert_eq!(Ok(time), string_to_timestamp(&s));
-    }
-}
-
-#[test]
-fn test_find_source_directory_in_iter() {
-    let already_visited = FxHashSet::default();
-
-    // Find newest
-    assert_eq!(find_source_directory_in_iter(
-        vec![PathBuf::from("crate-dir/s-3234-0000-svh"),
-             PathBuf::from("crate-dir/s-2234-0000-svh"),
-             PathBuf::from("crate-dir/s-1234-0000-svh")].into_iter(), &already_visited),
-        Some(PathBuf::from("crate-dir/s-3234-0000-svh")));
-
-    // Filter out "-working"
-    assert_eq!(find_source_directory_in_iter(
-        vec![PathBuf::from("crate-dir/s-3234-0000-working"),
-             PathBuf::from("crate-dir/s-2234-0000-svh"),
-             PathBuf::from("crate-dir/s-1234-0000-svh")].into_iter(), &already_visited),
-        Some(PathBuf::from("crate-dir/s-2234-0000-svh")));
-
-    // Handle empty
-    assert_eq!(find_source_directory_in_iter(vec![].into_iter(), &already_visited),
-               None);
-
-    // Handle only working
-    assert_eq!(find_source_directory_in_iter(
-        vec![PathBuf::from("crate-dir/s-3234-0000-working"),
-             PathBuf::from("crate-dir/s-2234-0000-working"),
-             PathBuf::from("crate-dir/s-1234-0000-working")].into_iter(), &already_visited),
-        None);
-}
diff --git a/src/librustc_incremental/persist/fs/tests.rs b/src/librustc_incremental/persist/fs/tests.rs
new file mode 100644
index 00000000000..09c2fc14638
--- /dev/null
+++ b/src/librustc_incremental/persist/fs/tests.rs
@@ -0,0 +1,65 @@
+use super::*;
+
+#[test]
+fn test_all_except_most_recent() {
+    assert_eq!(all_except_most_recent(
+        vec![
+            (UNIX_EPOCH + Duration::new(4, 0), PathBuf::from("4"), None),
+            (UNIX_EPOCH + Duration::new(1, 0), PathBuf::from("1"), None),
+            (UNIX_EPOCH + Duration::new(5, 0), PathBuf::from("5"), None),
+            (UNIX_EPOCH + Duration::new(3, 0), PathBuf::from("3"), None),
+            (UNIX_EPOCH + Duration::new(2, 0), PathBuf::from("2"), None),
+        ]).keys().cloned().collect::<FxHashSet<PathBuf>>(),
+        vec![
+            PathBuf::from("1"),
+            PathBuf::from("2"),
+            PathBuf::from("3"),
+            PathBuf::from("4"),
+        ].into_iter().collect::<FxHashSet<PathBuf>>()
+    );
+
+    assert_eq!(all_except_most_recent(
+        vec![
+        ]).keys().cloned().collect::<FxHashSet<PathBuf>>(),
+        FxHashSet::default()
+    );
+}
+
+#[test]
+fn test_timestamp_serialization() {
+    for i in 0 .. 1_000u64 {
+        let time = UNIX_EPOCH + Duration::new(i * 1_434_578, (i as u32) * 239_000);
+        let s = timestamp_to_string(time);
+        assert_eq!(Ok(time), string_to_timestamp(&s));
+    }
+}
+
+#[test]
+fn test_find_source_directory_in_iter() {
+    let already_visited = FxHashSet::default();
+
+    // Find newest
+    assert_eq!(find_source_directory_in_iter(
+        vec![PathBuf::from("crate-dir/s-3234-0000-svh"),
+             PathBuf::from("crate-dir/s-2234-0000-svh"),
+             PathBuf::from("crate-dir/s-1234-0000-svh")].into_iter(), &already_visited),
+        Some(PathBuf::from("crate-dir/s-3234-0000-svh")));
+
+    // Filter out "-working"
+    assert_eq!(find_source_directory_in_iter(
+        vec![PathBuf::from("crate-dir/s-3234-0000-working"),
+             PathBuf::from("crate-dir/s-2234-0000-svh"),
+             PathBuf::from("crate-dir/s-1234-0000-svh")].into_iter(), &already_visited),
+        Some(PathBuf::from("crate-dir/s-2234-0000-svh")));
+
+    // Handle empty
+    assert_eq!(find_source_directory_in_iter(vec![].into_iter(), &already_visited),
+               None);
+
+    // Handle only working
+    assert_eq!(find_source_directory_in_iter(
+        vec![PathBuf::from("crate-dir/s-3234-0000-working"),
+             PathBuf::from("crate-dir/s-2234-0000-working"),
+             PathBuf::from("crate-dir/s-1234-0000-working")].into_iter(), &already_visited),
+        None);
+}
diff --git a/src/tools/tidy/src/unit_tests.rs b/src/tools/tidy/src/unit_tests.rs
index f1822ea3435..79ccc11a69a 100644
--- a/src/tools/tidy/src/unit_tests.rs
+++ b/src/tools/tidy/src/unit_tests.rs
@@ -29,7 +29,6 @@ pub fn check(root_path: &Path, bad: &mut bool) {
         "liballoc",
         "librustc",
         "librustc_data_structures",
-        "librustc_incremental/persist",
         "librustdoc",
         "libstd",
         "libsyntax",