Merge #857: Check results in the DB tests

a1a70a5 Check results in the DB tests (Silvestrs Timofejevs)

Pull request description:

  ### Description

  Checksum test was giving a false positive due to ignoring the return value.

  Other tests were giving assertion fail later in the test, rather than an error on failed method call, thus making it more challenging to debug the issue.

  These have been discovered, when implementing PostgreSQL backend in a downstream fork.

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing
  * [x] I ran all `sqlite` and `key-value-db` tests successfully

ACKs for top commit:
  danielabrozzoni:
    ACK a1a70a5

Tree-SHA512: d3542cdd9f5f76f8318910261dbeb9cdcc9d4f26e9852e7aad7419c4abdf269d030b72bb21ee34a9dd314d2fa8433f1a6a9f1338a62699e5d8b6764c03067904

src/database/mod.rs

@@ -487,7 +487,7 @@ pub mod test {
 
         assert!(res.is_none());
 
-        let _res = db.set_script_pubkey(&script, keychain, path);
+        db.set_script_pubkey(&script, keychain, path).unwrap();
         let (chain, child) = db.del_path_from_script_pubkey(&script).unwrap().unwrap();
 
         assert_eq!(chain, keychain);
@@ -620,13 +620,13 @@ pub mod test {
     pub fn test_del_last_index<D: Database>(mut db: D) {
         let keychain = KeychainKind::External;
 
-        let _res = db.increment_last_index(keychain);
+        db.increment_last_index(keychain).unwrap();
 
         let res = db.get_last_index(keychain).unwrap().unwrap();
 
         assert_eq!(res, 0);
 
-        let _res = db.increment_last_index(keychain);
+        db.increment_last_index(keychain).unwrap();
 
         let res = db.del_last_index(keychain).unwrap().unwrap();
 
@@ -640,7 +640,7 @@ pub mod test {
         // insert checksum associated to keychain
         let checksum = "1cead456".as_bytes();
         let keychain = KeychainKind::External;
-        let _res = db.check_descriptor_checksum(keychain, checksum);
+        db.check_descriptor_checksum(keychain, checksum).unwrap();
 
         // check if `check_descriptor_checksum` throws
         // `Error::ChecksumMismatch` error if the