diff --git a/aead/src/dev.rs b/aead/src/dev.rs
index b128014bd..39d83db95 100644
--- a/aead/src/dev.rs
+++ b/aead/src/dev.rs
@@ -1,6 +1,12 @@
 //! Development-related functionality
 pub use blobby;
 
+#[cfg(all(feature = "alloc", feature = "inout"))]
+use {
+    crate::Tag, alloc::vec, alloc::vec::Vec, core::fmt, crypto_common::typenum::Unsigned,
+    inout::InOutBuf,
+};
+
 /// Define AEAD test
 #[macro_export]
 macro_rules! new_test {
@@ -45,6 +51,8 @@ macro_rules! new_test {
                 if res != pt {
                     return Err("decrypted data is different from target plaintext");
                 }
+
+                $crate::dev::new_test_impl_inout(cipher, nonce, aad, pt, ct, pass)?;
                 Ok(())
             }
 
@@ -75,3 +83,127 @@ macro_rules! new_test {
         }
     };
 }
+
+/// Helper to run tests against the inout API.
+#[cfg(not(all(feature = "alloc", feature = "inout")))]
+pub fn new_test_impl_inout<T: crate::AeadCore>(
+    _cipher: T,
+    _nonce: &crate::Nonce<T>,
+    _aad: &[u8],
+    _pt: &[u8],
+    _ct: &[u8],
+    _pass: bool,
+) -> Result<(), &'static str> {
+    Ok(())
+}
+
+/// Helper to run tests against the inout API.
+#[cfg(all(feature = "alloc", feature = "inout"))]
+pub fn new_test_impl_inout<T: crate::AeadInOut>(
+    cipher: T,
+    nonce: &crate::Nonce<T>,
+    aad: &[u8],
+    pt: &[u8],
+    ct: &[u8],
+    pass: bool,
+) -> Result<(), &'static str> {
+    // Here we assume this is a postfix tagged AEAD
+    let (ciphertext, expected_tag) = ct.split_at(ct.len() - T::TagSize::to_usize());
+    let expected_tag = Tag::<T>::try_from(expected_tag).expect("invariant violation");
+
+    if !pass {
+        let mut payload = MockBuffer::from(ciphertext);
+        let res = cipher.decrypt_inout_detached(nonce, aad, payload.to_in_out_buf(), &expected_tag);
+        if res.is_ok() {
+            return Err("Decryption must return an error");
+        }
+        return Ok(());
+    }
+
+    let mut payload = MockBuffer::from(pt);
+    let tag = cipher
+        .encrypt_inout_detached(nonce, aad, payload.to_in_out_buf())
+        .map_err(|_| "encryption failure")?;
+
+    // Here we assume this is a postfix tagged AEAD
+    let (ciphertext, _tag) = ct.split_at(ct.len() - T::TagSize::to_usize());
+    if payload.as_ref() != ciphertext {
+        return Err("encrypted data is different from target ciphertext");
+    }
+
+    let mut payload = MockBuffer::from(ciphertext);
+    cipher
+        .decrypt_inout_detached(nonce, aad, payload.to_in_out_buf(), &tag)
+        .map_err(|_| "decryption failure")?;
+
+    if payload.as_ref() != pt {
+        return Err("decrypted data is different from target plaintext");
+    }
+
+    Ok(())
+}
+
+/// [`MockBuffer`] is meant for testing InOut-backed APIs.
+///
+/// It will split the initial buffer in two different backing buffers. The out buffer will be
+/// zeroed.
+#[cfg(all(feature = "alloc", feature = "inout"))]
+pub struct MockBuffer {
+    in_buf: Vec<u8>,
+    out_buf: Vec<u8>,
+}
+
+#[cfg(all(feature = "alloc", feature = "inout"))]
+impl AsRef<[u8]> for MockBuffer {
+    fn as_ref(&self) -> &[u8] {
+        &self.out_buf
+    }
+}
+
+#[cfg(all(feature = "alloc", feature = "inout"))]
+impl From<&[u8]> for MockBuffer {
+    fn from(buf: &[u8]) -> Self {
+        Self {
+            in_buf: buf.to_vec(),
+            out_buf: vec![0u8; buf.len()],
+        }
+    }
+}
+
+#[cfg(all(feature = "alloc", feature = "inout"))]
+impl From<Vec<u8>> for MockBuffer {
+    fn from(buf: Vec<u8>) -> Self {
+        Self {
+            out_buf: vec![0u8; buf.len()],
+            in_buf: buf,
+        }
+    }
+}
+
+#[cfg(all(feature = "alloc", feature = "inout"))]
+impl MockBuffer {
+    /// Get an [`InOutBuf`] from a [`MockBuffer`]
+    pub fn to_in_out_buf(&mut self) -> InOutBuf<'_, '_, u8> {
+        InOutBuf::new(self.in_buf.as_slice(), self.out_buf.as_mut_slice())
+            .expect("Invariant violation")
+    }
+
+    /// Return the length of the payload
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.in_buf.len()
+    }
+
+    /// Is the payload empty?
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.in_buf.is_empty()
+    }
+}
+
+#[cfg(all(feature = "alloc", feature = "inout"))]
+impl fmt::Debug for MockBuffer {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "MockBuffer {{...}}")
+    }
+}