try to really fix tests on macOS

Author: RalfJung

test-cargo-miri/tests/test.rs

@@ -20,15 +20,18 @@ fn fixed_rng() {
 }
 
 #[test]
-#[cfg(not(target_os="macos"))] // FIXME entropy does not work on macOS
 fn entropy_rng() {
-    // Use this opportunity to test querying the RNG (needs an external crate, hence tested here and not in the compiletest suite)
-    let mut rng = SmallRng::from_entropy();
-    let _val = rng.gen::<i32>();
+    #[cfg(not(target_os="macos"))] // FIXME entropy does not work on macOS
+    // (Not disabling the entire test as that would change the output.)
+    {
+        // Use this opportunity to test querying the RNG (needs an external crate, hence tested here and not in the compiletest suite)
+        let mut rng = SmallRng::from_entropy();
+        let _val = rng.gen::<i32>();
 
-    // Also try per-thread RNG.
-    let mut rng = rand::thread_rng();
-    let _val = rng.gen::<i32>();
+        // Also try per-thread RNG.
+        let mut rng = rand::thread_rng();
+        let _val = rng.gen::<i32>();
+    }
 }
 
 // A test that won't work on miri