diff --git a/src/traits.rs b/src/traits.rs
index 7c9f183..9626655 100644
--- a/src/traits.rs
+++ b/src/traits.rs
@@ -18,6 +18,7 @@ use typenum::Unsigned;
 ///
 /// NOTE: This trait is effectively sealed and can not be implemented by third-party crates.
 /// It is implemented only for a number of types defined in [`typenum::consts`].
+#[diagnostic::on_unimplemented(note = "size may not be supported (see RustCrypto/hybrid-array#66)")]
 pub unsafe trait ArraySize: Unsigned + Debug {
     /// Array type which corresponds to this size.
     ///
@@ -197,3 +198,82 @@ impl<T> sealed::Sealed for [T] {}
 mod sealed {
     pub trait Sealed {}
 }
+
+#[cfg(test)]
+mod tests {
+    use super::{AsArrayMut, AsArrayRef, SliceExt};
+    use crate::{
+        Array,
+        sizes::{U2, U3},
+    };
+
+    type A = Array<u8, U2>;
+
+    #[test]
+    fn core_as_array_ref() {
+        assert_eq!([1, 2, 3].as_array_ref(), &Array([1, 2, 3]));
+    }
+
+    #[test]
+    fn core_as_array_mut() {
+        assert_eq!([1, 2, 3].as_array_mut(), &Array([1, 2, 3]));
+    }
+
+    #[test]
+    fn slice_as_hybrid_array() {
+        assert_eq!([1, 2].as_hybrid_array::<U3>(), None);
+        assert_eq!([1, 2, 3].as_hybrid_array::<U3>(), Some(&Array([1, 2, 3])));
+        assert_eq!([1, 2, 3, 4].as_hybrid_array::<U3>(), None);
+    }
+
+    #[test]
+    fn slice_as_mut_hybrid_array() {
+        assert_eq!([1, 2].as_mut_hybrid_array::<U3>(), None);
+        assert_eq!(
+            [1, 2, 3].as_mut_hybrid_array::<U3>(),
+            Some(&mut Array([1, 2, 3]))
+        );
+        assert_eq!([1, 2, 3, 4].as_mut_hybrid_array::<U3>(), None);
+    }
+
+    #[test]
+    fn slice_as_hybrid_chunks() {
+        let (slice_empty, rem_empty): (&[A], &[u8]) = [].as_hybrid_chunks::<U2>();
+        assert!(slice_empty.is_empty());
+        assert!(rem_empty.is_empty());
+
+        let (slice_one, rem_one) = [1].as_hybrid_chunks::<U2>();
+        assert!(slice_one.is_empty());
+        assert_eq!(rem_one, &[1]);
+
+        let (slice_aligned, rem_aligned) = [1u8, 2].as_hybrid_chunks::<U2>();
+        assert_eq!(slice_aligned, &[Array([1u8, 2])]);
+        assert_eq!(rem_aligned, &[]);
+
+        let (slice_unaligned, rem_unaligned) = [1u8, 2, 3].as_hybrid_chunks::<U2>();
+        assert_eq!(slice_unaligned, &[Array([1u8, 2])]);
+        assert_eq!(rem_unaligned, &[3]);
+    }
+
+    #[test]
+    fn slice_as_hybrid_chunks_mut() {
+        let (slice_empty, rem_empty): (&mut [A], &mut [u8]) = [].as_hybrid_chunks_mut::<U2>();
+        assert!(slice_empty.is_empty());
+        assert!(rem_empty.is_empty());
+
+        let mut arr1 = [1];
+        let (slice_one, rem_one) = arr1.as_hybrid_chunks_mut::<U2>();
+        assert!(slice_one.is_empty());
+        assert_eq!(rem_one, &[1]);
+
+        let mut arr2 = [1u8, 2];
+        let (slice_aligned, rem_aligned) = arr2.as_hybrid_chunks_mut::<U2>();
+        assert_eq!(slice_aligned, &mut [Array([1u8, 2])]);
+        assert_eq!(rem_aligned, &mut []);
+
+        let mut arr3 = [1u8, 2, 3];
+        let (slice_unaligned, rem_unaligned) = arr3.as_hybrid_chunks_mut::<U2>();
+        assert_eq!(slice_unaligned, &mut [Array([1u8, 2])]);
+        assert_eq!(rem_unaligned, &mut [3]);
+    }
+}