Remove unnecessary mut on R_TEST_LOCK (#675)

Author: lionel-

crates/ark/src/r_task.rs

@@ -147,7 +147,7 @@ where
 {
     // Escape hatch for unit tests
     if stdext::IS_TESTING {
-        let _lock = unsafe { harp::fixtures::R_TEST_LOCK.lock() };
+        let _lock = harp::fixtures::R_TEST_LOCK.lock();
         r_test_init();
         return f();
     }
@@ -255,7 +255,7 @@ where
 {
     // Escape hatch for unit tests
     if stdext::IS_TESTING {
-        let _lock = unsafe { harp::fixtures::R_TEST_LOCK.lock() };
+        let _lock = harp::fixtures::R_TEST_LOCK.lock();
         futures::executor::block_on(fun());
         return;
     }

crates/harp/src/fixtures/mod.rs

@@ -23,7 +23,7 @@ use crate::R_MAIN_THREAD_ID;
 
 // FIXME: Needs to be a reentrant lock for idle tasks. We can probably do better
 // though.
-pub static mut R_TEST_LOCK: parking_lot::ReentrantMutex<()> = parking_lot::ReentrantMutex::new(());
+pub static R_TEST_LOCK: parking_lot::ReentrantMutex<()> = parking_lot::ReentrantMutex::new(());
 
 static INIT: Once = Once::new();
 
@@ -35,7 +35,7 @@ static INIT: Once = Once::new();
 /// `ark::r_task()` in Ark tests so that Ark initialisation also takes place.
 #[cfg(test)]
 pub(crate) fn r_task<F: FnOnce()>(f: F) {
-    let guard = unsafe { R_TEST_LOCK.lock() };
+    let guard = R_TEST_LOCK.lock();
 
     r_test_init();
     f();