Add missing tests for c/r_return_mut

Author: sbrocket

tests/ffi/tests.cc

@@ -380,6 +380,13 @@ extern "C" const char *cxx_run_test() noexcept {
   ASSERT(cxx_test_suite_r_is_correct(&*r_return_box()));
   ASSERT(r_return_unique_ptr()->get() == 2020);
   ASSERT(r_return_ref(Shared{2020}) == 2020);
+  {
+    Shared shared{2019};
+    size_t &mut_z = r_return_mut(shared);
+    ASSERT(mut_z == 2019);
+    mut_z = 2020;
+    ASSERT(r_return_ref(shared) == 2020);
+  }
   ASSERT(std::string(r_return_str(Shared{2020})) == "2020");
   ASSERT(std::string(r_return_rust_string()) == "2020");
   ASSERT(*r_return_unique_ptr_string() == "2020");

tests/test.rs

@@ -21,13 +21,21 @@ macro_rules! check {
 
 #[test]
 fn test_c_return() {
-    let shared = ffi::Shared { z: 2020 };
+    let mut shared = ffi::Shared { z: 2020 };
 
     assert_eq!(2020, ffi::c_return_primitive());
     assert_eq!(2020, ffi::c_return_shared().z);
     assert_eq!(2020, *ffi::c_return_box());
     ffi::c_return_unique_ptr();
     assert_eq!(2020, *ffi::c_return_ref(&shared));
+
+    {
+        shared.z = 2019;
+        let mut_z = ffi::c_return_mut(&mut shared);
+        assert_eq!(2019, *mut_z);
+        *mut_z = 2020;
+    }
+
     assert_eq!("2020", ffi::c_return_str(&shared));
     assert_eq!(b"2020\0", ffi::c_return_sliceu8(&shared));
     assert_eq!("2020", ffi::c_return_rust_string());