hash_types: add unit tests for display of all hash types in the library

This can be checked against the 0.29.x branch, and against the commit
prior to #1659 (40c246743b^) and you will see that it is consistent
EXCEPT:

* In rust-bitcoin 0.29.x we did not have multiple sighash types, only
  `Sighash`; we now have `LegacySighash`, `SegwitV0Sighash`, and
  `TapSighash`.
* In #1565 we deliberately changed the display direction of the
  sighashes, to match BIP 143.

Fixes #2495.

bitcoin/src/hash_types.rs

@@ -9,3 +9,83 @@ pub use crate::{
     BlockHash, FilterHash, FilterHeader, TxMerkleNode, Txid, WitnessCommitment, WitnessMerkleNode,
     Wtxid,
 };
+
+#[cfg(test)]
+mod tests {
+    use crate::hashes::Hash;
+    use super::*;
+
+    use crate::{LegacySighash, SegwitV0Sighash, TapSighash, PubkeyHash, WPubkeyHash, WScriptHash, ScriptHash, XKeyIdentifier};
+
+    #[test]
+    fn hash_display() {
+        assert_eq!(
+            Txid::hash(&[]).to_string(),
+            "56944c5d3f98413ef45cf54545538103cc9f298e0575820ad3591376e2e0f65d",
+        );
+
+        assert_eq!(
+            Wtxid::hash(&[]).to_string(),
+            "56944c5d3f98413ef45cf54545538103cc9f298e0575820ad3591376e2e0f65d",
+        );
+        assert_eq!(
+            BlockHash::hash(&[]).to_string(),
+            "56944c5d3f98413ef45cf54545538103cc9f298e0575820ad3591376e2e0f65d",
+        );
+        assert_eq!(
+            LegacySighash::hash(&[]).to_string(),
+            "5df6e0e2761359d30a8275058e299fcc0381534545f55cf43e41983f5d4c9456",
+        );
+        assert_eq!(
+            SegwitV0Sighash::hash(&[]).to_string(),
+            "5df6e0e2761359d30a8275058e299fcc0381534545f55cf43e41983f5d4c9456",
+        );
+        assert_eq!(
+            TapSighash::hash(&[]).to_string(),
+            "dabc11914abcd8072900042a2681e52f8dba99ce82e224f97b5fdb7cd4b9c803",
+        );
+
+        assert_eq!(
+            PubkeyHash::hash(&[]).to_string(),
+            "b472a266d0bd89c13706a4132ccfb16f7c3b9fcb",
+        );
+        assert_eq!(
+            ScriptHash::hash(&[]).to_string(),
+            "b472a266d0bd89c13706a4132ccfb16f7c3b9fcb",
+        );
+        assert_eq!(
+            WPubkeyHash::hash(&[]).to_string(),
+            "b472a266d0bd89c13706a4132ccfb16f7c3b9fcb",
+        );
+        assert_eq!(
+            WScriptHash::hash(&[]).to_string(),
+            "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+        );
+
+        assert_eq!(
+            TxMerkleNode::hash(&[]).to_string(),
+            "56944c5d3f98413ef45cf54545538103cc9f298e0575820ad3591376e2e0f65d",
+        );
+        assert_eq!(
+            WitnessMerkleNode::hash(&[]).to_string(),
+            "56944c5d3f98413ef45cf54545538103cc9f298e0575820ad3591376e2e0f65d",
+        );
+        assert_eq!(
+            WitnessCommitment::hash(&[]).to_string(),
+            "56944c5d3f98413ef45cf54545538103cc9f298e0575820ad3591376e2e0f65d",
+        );
+        assert_eq!(
+            XKeyIdentifier::hash(&[]).to_string(),
+            "b472a266d0bd89c13706a4132ccfb16f7c3b9fcb",
+        );
+
+        assert_eq!(
+            FilterHash::hash(&[]).to_string(),
+            "56944c5d3f98413ef45cf54545538103cc9f298e0575820ad3591376e2e0f65d",
+        );
+        assert_eq!(
+            FilterHeader::hash(&[]).to_string(),
+            "56944c5d3f98413ef45cf54545538103cc9f298e0575820ad3591376e2e0f65d",
+        );
+    }
+}