diff --git a/um_crypto/qmc/src/lib.rs b/um_crypto/qmc/src/lib.rs
index 6110d33..494fa00 100644
--- a/um_crypto/qmc/src/lib.rs
+++ b/um_crypto/qmc/src/lib.rs
@@ -9,3 +9,17 @@ pub enum QmcCryptoError {
     #[error("QMC V2/Map Cipher: Key is empty")]
     QMCV2MapKeyEmpty,
 }
+
+#[cfg(test)]
+mod test {
+    pub fn generate_key(len: usize) -> Vec<u8> {
+        (1..=len).map(|i| i as u8).collect()
+    }
+
+    #[cfg(test)]
+    pub fn generate_key_128() -> [u8; 128] {
+        generate_key(128)
+            .try_into()
+            .expect("failed to make test key")
+    }
+}
diff --git a/um_crypto/qmc/src/v1/cipher.rs b/um_crypto/qmc/src/v1/cipher.rs
index 7d35e2f..f473dc3 100644
--- a/um_crypto/qmc/src/v1/cipher.rs
+++ b/um_crypto/qmc/src/v1/cipher.rs
@@ -11,3 +11,30 @@ pub fn qmc1_transform(key: &[u8; V1_KEY_SIZE], value: u8, offset: usize) -> u8 {
 
     value ^ key[offset % V1_KEY_SIZE]
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::test::generate_key_128;
+
+    #[test]
+    fn test_decode_start() {
+        let test_key = generate_key_128();
+        let mut data = *b"igohj&pg{fo";
+        for (i, datum) in data.iter_mut().enumerate() {
+            *datum = qmc1_transform(&test_key, *datum, i);
+        }
+        assert_eq!(data, *b"hello world");
+    }
+    #[test]
+    fn test_decode_boundary() {
+        let test_key = generate_key_128();
+        let mut data = [
+            0x13, 0x19, 0x11, 0x12, 0x10, 0xa0, 0x75, 0x6c, 0x76, 0x69, 0x62,
+        ];
+        for (i, datum) in data.iter_mut().enumerate() {
+            *datum = qmc1_transform(&test_key, *datum, 0x7FFA + i);
+        }
+        assert_eq!(data, *b"hello world");
+    }
+}