Implement custom Debug for Sha256dChecksum

Relates to #63

zebra-chain/src/block.rs

@@ -161,7 +161,7 @@ mod tests {
     use crate::sha256d_writer::Sha256dWriter;
 
     #[test]
-    fn test_blockheaderhash_debug() {
+    fn blockheaderhash_debug() {
         let preimage = b"foo bar baz";
         let mut sha_writer = Sha256dWriter::default();
         let _ = sha_writer.write_all(preimage);

zebra-chain/src/types.rs

@@ -1,7 +1,10 @@
 //! Newtype wrappers for primitive data types with semantic meaning.
 
+use hex;
+use std::fmt;
+
 /// A 4-byte checksum using truncated double-SHA256 (two rounds of SHA256).
-#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+#[derive(Copy, Clone, Eq, PartialEq)]
 pub struct Sha256dChecksum(pub [u8; 4]);
 
 impl<'a> From<&'a [u8]> for Sha256dChecksum {
@@ -15,6 +18,14 @@ impl<'a> From<&'a [u8]> for Sha256dChecksum {
     }
 }
 
+impl fmt::Debug for Sha256dChecksum {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("Sha256dChecksum")
+            .field(&hex::encode(&self.0))
+            .finish()
+    }
+}
+
 /// A u32 which represents a block height value.
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub struct BlockHeight(pub u32);
@@ -31,4 +42,12 @@ mod tests {
         let expected = Sha256dChecksum([0x95, 0x95, 0xc9, 0xdf]);
         assert_eq!(checksum, expected);
     }
+
+    #[test]
+    fn sha256d_checksum_debug() {
+        let input = b"hello";
+        let checksum = Sha256dChecksum::from(&input[..]);
+
+        assert_eq!(format!("{:?}", checksum), "Sha256dChecksum(\"9595c9df\")");
+    }
 }