Add unit tests

Sources/DataLiteCore/Classes/Connection+Location.swift

@@ -7,7 +7,7 @@ extension Connection {
     /// - ``file(path:)``: A database at a specific file path or URI (persistent).
     /// - ``inMemory``: An in-memory database that exists only in RAM.
     /// - ``temporary``: A temporary on-disk database deleted when the connection closes.
-    public enum Location {
+    public enum Location: Sendable {
         /// A database stored at a given file path or URI.
         ///
         /// Use this for persistent databases located on disk or referenced via SQLite URI.

Sources/DataLiteCore/Classes/Connection.swift

@@ -152,7 +152,7 @@ extension Connection: ConnectionProtocol {
             sqlite3_key(connection, key.keyValue, key.length)
         }
         guard status == SQLITE_OK else {
-            throw SQLiteError(connection)
+            throw SQLiteError(code: status, message: "")
         }
     }
     
@@ -163,13 +163,15 @@ extension Connection: ConnectionProtocol {
             sqlite3_rekey(connection, key.keyValue, key.length)
         }
         guard status == SQLITE_OK else {
-            throw SQLiteError(connection)
+            throw SQLiteError(code: status, message: "")
         }
     }
     
     public func add(delegate: any ConnectionDelegate) {
-        delegates.append(.init(delegate: delegate))
-        delegates.removeAll { $0.delegate == nil }
+        if !delegates.contains(where: { $0.delegate === delegate }) {
+            delegates.append(.init(delegate: delegate))
+            delegates.removeAll { $0.delegate == nil }
+        }
     }
     
     public func remove(delegate: any ConnectionDelegate) {
@@ -179,8 +181,10 @@ extension Connection: ConnectionProtocol {
     }
     
     public func add(trace delegate: any ConnectionTraceDelegate) {
-        traceDelegates.append(.init(delegate: delegate))
-        traceDelegates.removeAll { $0.delegate == nil }
+        if !traceDelegates.contains(where: { $0.delegate === delegate }) {
+            traceDelegates.append(.init(delegate: delegate))
+            traceDelegates.removeAll { $0.delegate == nil }
+        }
     }
     
     public func remove(trace delegate: any ConnectionTraceDelegate) {

Sources/DataLiteCore/Classes/Statement.swift

@@ -51,6 +51,19 @@ public final class Statement {
 // MARK: - StatementProtocol
 
 extension Statement: StatementProtocol {
+    public var sql: String? {
+        let cSQL = sqlite3_sql(statement)
+        guard let cSQL else { return nil }
+        return String(cString: cSQL)
+    }
+    
+    public var expandedSQL: String? {
+        let cSQL = sqlite3_expanded_sql(statement)
+        defer { sqlite3_free(cSQL) }
+        guard let cSQL else { return nil }
+        return String(cString: cSQL)
+    }
+    
     public func parameterCount() -> Int32 {
         sqlite3_bind_parameter_count(statement)
     }