diff --git a/src/bitkmer.rs b/src/bitkmer.rs
index 1421a1f..5f3c913 100644
--- a/src/bitkmer.rs
+++ b/src/bitkmer.rs
@@ -275,9 +275,9 @@ mod tests {
 
     #[test]
     fn test_bitmer_to_bytes() {
-        assert_eq!(bitmer_to_bytes((1 as BitKmerSeq, 1)), b"C".to_vec());
-        assert_eq!(bitmer_to_bytes((60 as BitKmerSeq, 3)), b"TTA".to_vec());
-        assert_eq!(bitmer_to_bytes((0 as BitKmerSeq, 3)), b"AAA".to_vec());
+        assert_eq!(bitmer_to_bytes((1 as BitKmerSeq, 1)), b"C");
+        assert_eq!(bitmer_to_bytes((60 as BitKmerSeq, 3)), b"TTA");
+        assert_eq!(bitmer_to_bytes((0 as BitKmerSeq, 3)), b"AAA");
     }
 
     pub fn bytes_to_bitmer(kmer: &[u8]) -> BitKmer {
diff --git a/src/sequence.rs b/src/sequence.rs
index dc38f9a..da9c297 100644
--- a/src/sequence.rs
+++ b/src/sequence.rs
@@ -326,20 +326,32 @@ mod tests {
 
     #[test]
     fn test_normalize() {
-        assert_eq!(normalize(b"ACGTU", false), Some(b"ACGTT".to_vec()));
-        assert_eq!(normalize(b"acgtu", false), Some(b"ACGTT".to_vec()));
+        assert_eq!(
+            normalize(b"ACGTU", false).as_deref(),
+            Some(b"ACGTT".as_slice())
+        );
+        assert_eq!(
+            normalize(b"acgtu", false).as_deref(),
+            Some(b"ACGTT".as_slice())
+        );
 
-        assert_eq!(normalize(b"N.N-N~N N", false), Some(b"N-N-N-NN".to_vec()));
+        assert_eq!(
+            normalize(b"N.N-N~N N", false).as_deref(),
+            Some(b"N-N-N-NN".as_slice())
+        );
 
         assert_eq!(normalize(b"BDHVRYSWKM", true), None);
-        assert_eq!(normalize(b"bdhvryswkm", true), Some(b"BDHVRYSWKM".to_vec()));
         assert_eq!(
-            normalize(b"BDHVRYSWKM", false),
-            Some(b"NNNNNNNNNN".to_vec())
+            normalize(b"bdhvryswkm", true).as_deref(),
+            Some(b"BDHVRYSWKM".as_slice())
+        );
+        assert_eq!(
+            normalize(b"BDHVRYSWKM", false).as_deref(),
+            Some(b"NNNNNNNNNN".as_slice())
         );
         assert_eq!(
-            normalize(b"bdhvryswkm", false),
-            Some(b"NNNNNNNNNN".to_vec())
+            normalize(b"bdhvryswkm", false).as_deref(),
+            Some(b"NNNNNNNNNN".as_slice())
         );
     }
 
@@ -353,11 +365,11 @@ mod tests {
 
     #[test]
     fn can_canonicalize() {
-        assert_eq!(canonical(b"A"), Cow::Borrowed(b"A"));
-        assert_eq!(canonical(b"T"), Cow::Owned::<[u8]>(b"A".to_vec()));
-        assert_eq!(canonical(b"AAGT"), Cow::Borrowed(b"AAGT"));
-        assert_eq!(canonical(b"ACTT"), Cow::Owned::<[u8]>(b"AAGT".to_vec()));
-        assert_eq!(canonical(b"GC"), Cow::Borrowed(b"GC"));
+        assert_eq!(canonical(b"A").as_ref(), b"A");
+        assert_eq!(canonical(b"T").as_ref(), b"A");
+        assert_eq!(canonical(b"AAGT").as_ref(), b"AAGT");
+        assert_eq!(canonical(b"ACTT").as_ref(), b"AAGT");
+        assert_eq!(canonical(b"GC").as_ref(), b"GC");
     }
 
     #[test]