Merge bitcoindevkit/bdk#661: Test: No address reuse for single descriptor

2c02a44586c67d1ec9720f17a3748f28c1d18643 Test: No address reuse for single descriptor (志宇)

Pull request description:

  ### Description

  Just a simple new test.

  This test is to ensure there are no regressions when we later change
  internal logic of `Wallet`. A single descriptor wallet should always get
  a new address with `AddressIndex::New` even if we alternate grabbing
  internal/external keychains.

  I thought of adding this during work on #647

  ### 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

ACKs for top commit:
  danielabrozzoni:
    tACK 2c02a44586c67d1ec9720f17a3748f28c1d18643
  rajarshimaitra:
    tACK 2c02a44586c67d1ec9720f17a3748f28c1d18643

Tree-SHA512: d065ae0979dc3ef7c26d6dfc19c88498e4bf17cc908e4f5677dcbf62ee59162e666cb00eb87b96d4c2557310960e3677eec7b6d907a5a4860cb7d2d74dba07b0

src/wallet/mod.rs

@@ -4499,6 +4499,34 @@ pub(crate) mod test {
         );
     }
 
+    #[test]
+    fn test_get_address_no_reuse_single_descriptor() {
+        use crate::descriptor::template::Bip84;
+        use std::collections::HashSet;
+
+        let key = bitcoin::util::bip32::ExtendedPrivKey::from_str("tprv8ZgxMBicQKsPcx5nBGsR63Pe8KnRUqmbJNENAfGftF3yuXoMMoVJJcYeUw5eVkm9WBPjWYt6HMWYJNesB5HaNVBaFc1M6dRjWSYnmewUMYy").unwrap();
+        let wallet = Wallet::new(
+            Bip84(key, KeychainKind::External),
+            None,
+            Network::Regtest,
+            MemoryDatabase::default(),
+        )
+        .unwrap();
+
+        let mut used_set = HashSet::new();
+
+        (0..3).for_each(|_| {
+            let external_addr = wallet.get_address(AddressIndex::New).unwrap().address;
+            assert!(used_set.insert(external_addr));
+
+            let internal_addr = wallet
+                .get_internal_address(AddressIndex::New)
+                .unwrap()
+                .address;
+            assert!(used_set.insert(internal_addr));
+        });
+    }
+
     #[test]
     fn test_taproot_psbt_populate_tap_key_origins() {
         let (wallet, _, _) = get_funded_wallet(get_test_tr_single_sig_xprv());