test: add offline tests for wallet new_or_load method

bdk-swift/Tests/BitcoinDevKitTests/OfflinePersistenceTests.swift

@@ -0,0 +1,40 @@
+import XCTest
+@testable import BitcoinDevKit
+
+private let descriptor = try! Descriptor(
+    descriptor: "wpkh(tprv8ZgxMBicQKsPf2qfrEygW6fdYseJDDrVnDv26PH5BHdvSuG6ecCbHqLVof9yZcMoM31z9ur3tTYbSnr1WBqbGX97CbXcmp5H6qeMpyvx35B/84h/1h/0h/0/*)", 
+    network: Network.signet
+)
+private let changeDescriptor = try! Descriptor(
+    descriptor: "wpkh(tprv8ZgxMBicQKsPf2qfrEygW6fdYseJDDrVnDv26PH5BHdvSuG6ecCbHqLVof9yZcMoM31z9ur3tTYbSnr1WBqbGX97CbXcmp5H6qeMpyvx35B/84h/1h/0h/1/*)", 
+    network: Network.signet
+)
+
+final class OfflinePersistenceTests: XCTestCase {
+    var dbFilePath: URL!
+
+    override func setUpWithError() throws {
+        super.setUp()
+        let currentDirectoryURL = URL(fileURLWithPath: FileManager.default.currentDirectoryPath)
+        let dbFileName = "pre_existing_wallet_persistence_test.sqlite"
+        dbFilePath = currentDirectoryURL.appendingPathComponent(dbFileName)
+    }
+
+    func testPersistence() throws {
+        let sqliteStore = try! SqliteStore(path: dbFilePath.path)
+        let initialChangeSet = try! sqliteStore.read()
+        XCTAssertTrue(initialChangeSet != nil, "ChangeSet should not be nil after loading a valid database")
+        
+        let wallet = try Wallet.newOrLoad(
+            descriptor: descriptor,
+            changeDescriptor: changeDescriptor,
+            changeSet: initialChangeSet,
+            network: .signet
+        )
+        let nextAddress: AddressInfo = wallet.revealNextAddress(keychain: KeychainKind.external)
+        print("Address: \(nextAddress)")
+
+        XCTAssertTrue(nextAddress.address.description == "tb1qan3lldunh37ma6c0afeywgjyjgnyc8uz975zl2")
+        XCTAssertTrue(nextAddress.index == 7)
+    }
+}