Fix the flaky test buck2/shed/static_interner

Summary:
The `test_disposition` test was sharing the static `STRING_INTERNER` variable with `test_intern,` and both tests used the string `"hello"`. When tests run in parallel, if `test_intern` runs first, it causes `test_disposition` to fail.

This fix adds a dedicated `TEST_DISPOSITION_STRING` interner to isolate the tests from each other.

It also move the test downside to separate from tests using `STRING_INTERNER`

Reviewed By: blackm00n

Differential Revision: D67626618

fbshipit-source-id: 6d51485f919a4c4b09608a7afe36242dbc405d41

shed/static_interner/src/lib.rs

@@ -311,17 +311,6 @@ mod tests {
         );
     }
 
-    #[test]
-    fn test_disposition() {
-        let (val, disposition) = STRING_INTERNER.observed_intern("hello".to_owned());
-        assert_eq!(val.to_string(), "hello".to_owned());
-        assert!(std::matches!(disposition, InternDisposition::Computed));
-
-        let (val, disposition) = STRING_INTERNER.observed_intern("hello".to_owned());
-        assert_eq!(val.to_string(), "hello".to_owned());
-        assert!(std::matches!(disposition, InternDisposition::Interned));
-    }
-
     // Make sure things work with reallocation.
     #[test]
     fn test_resize() {
@@ -351,6 +340,18 @@ mod tests {
         }
     }
 
+    static TEST_DISPOSITION_STRING: Interner<String> = Interner::new();
+    #[test]
+    fn test_disposition() {
+        let (val, disposition) = TEST_DISPOSITION_STRING.observed_intern("hello".to_owned());
+        assert_eq!(val.to_string(), "hello".to_owned());
+        assert!(std::matches!(disposition, InternDisposition::Computed));
+
+        let (val, disposition) = TEST_DISPOSITION_STRING.observed_intern("hello".to_owned());
+        assert_eq!(val.to_string(), "hello".to_owned());
+        assert!(std::matches!(disposition, InternDisposition::Interned));
+    }
+
     static TEST_GET_INTERNER: Interner<String> = Interner::new();
     #[test]
     fn test_get() {