Avoid indexing in test assertions

src/tests.rs

@@ -84,7 +84,7 @@ fn test_send_type_erased_vec_retains_send_elements_across_threads() {
     .join()
     .expect("worker thread panicked");
 
-    assert_eq!(values[0].get(), 42);
+    assert_eq!(values.first().map(Cell::get), Some(42));
 }
 
 #[test]
@@ -294,12 +294,18 @@ fn test_cast_type_success_and_mutation() {
     assert_guard_state(&guard, 2);
     assert!(guard.capacity() >= initial_cap);
 
-    let slice = guard.as_slice_mut();
-    slice[0] = 42;
+    let mutable_slice = guard.as_slice_mut();
+    assert_eq!(
+        mutable_slice.first_mut().map(|first| {
+            *first = 42;
+            *first
+        }),
+        Some(42)
+    );
 
-    let slice = guard.as_slice();
+    let immutable_slice = guard.as_slice();
     // Casting -2_i32 into u32 results in u32::MAX - 1 due to two's complement.
-    assert_eq!(slice, &[42, u32::MAX - 1]);
+    assert_eq!(immutable_slice, &[42, u32::MAX - 1]);
 
     let restored = guard.take();
     assert_eq!(restored, vec![42, u32::MAX - 1]);
@@ -511,7 +517,13 @@ fn test_guard_into_slice_mut() {
 
     let guard = unsafe { erased.cast_type::<i32>() };
     let slice = guard.into_slice_mut();
-    slice[0] = 99;
+    assert_eq!(
+        slice.first_mut().map(|first| {
+            *first = 99;
+            *first
+        }),
+        Some(99)
+    );
     assert_eq!(slice, &[99, 2]);
 }
 
@@ -522,7 +534,7 @@ fn test_guard_push() {
     let mut guard = erased.as_type::<i32>();
 
     guard.push(42);
-    assert_eq!(guard.with(|v| v[0]), 42);
+    assert_eq!(guard.with(|values| values.first().copied()), Some(42));
     assert_eq!(guard.length(), 1);
     assert_eq!(guard.as_slice(), &[42]);
 }