Update HashMap::try_reserve test to version from hashbrown

Author: Amanieu

library/std/src/collections/hash/map/tests.rs

@@ -828,11 +828,21 @@ fn test_try_reserve() {
         "usize::MAX should trigger an overflow!"
     );
 
-    assert_matches!(
-        empty_bytes.try_reserve(MAX_USIZE / 8).map_err(|e| e.kind()),
-        Err(AllocError { .. }),
-        "usize::MAX / 8 should trigger an OOM!"
-    );
+    if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_USIZE / 16).map_err(|e| e.kind()) {
+    } else {
+        // This may succeed if there is enough free memory. Attempt to
+        // allocate a few more hashmaps to ensure the allocation will fail.
+        let mut empty_bytes2: HashMap<u8, u8> = HashMap::new();
+        let _ = empty_bytes2.try_reserve(MAX_USIZE / 16);
+        let mut empty_bytes3: HashMap<u8, u8> = HashMap::new();
+        let _ = empty_bytes3.try_reserve(MAX_USIZE / 16);
+        let mut empty_bytes4: HashMap<u8, u8> = HashMap::new();
+        assert_matches!(
+            empty_bytes4.try_reserve(MAX_USIZE / 16).map_err(|e| e.kind()),
+            Err(AllocError { .. }),
+            "usize::MAX / 16 should trigger an OOM!"
+        );
+    }
 }
 
 #[test]