Address review comments

Signed-off-by: Tomasz Pietrek <[email protected]>

Sources/Nats/NatsConnection.swift

@@ -333,6 +333,9 @@ class ConnectionHandler: ChannelInboundHandler {
             user: self.auth?.user ?? "", pass: self.auth?.password ?? "",
             authToken: self.auth?.token ?? "", headers: true, noResponders: true)
 
+        if self.auth?.nkey != nil && self.auth?.nkeyPath != nil {
+            throw NatsConfigError("cannot use both nkey and nkeyPath")
+        }
         if let auth = self.auth, let credentialsPath = auth.credentialsPath {
             let credentials = try await URLSession.shared.data(from: credentialsPath).0
             guard let jwt = JwtUtils.parseDecoratedJWT(contents: credentials) else {

Tests/NatsTests/Integration/ConnectionTests.swift

@@ -41,6 +41,7 @@ class CoreNatsTests: XCTestCase {
         ("testRequest_noResponders", testRequest_noResponders),
         ("testRequest_timeout", testRequest_timeout),
         ("testNkeyAuth", testNkeyAuth),
+        ("testNkeyAuthFile", testNkeyAuthFile),
     ]
     var natsServer = NatsServer()
 
@@ -402,6 +403,29 @@ class CoreNatsTests: XCTestCase {
         let subscribe = try await client.subscribe(subject: "foo").makeAsyncIterator()
         try await client.publish("data".data(using: .utf8)!, subject: "foo")
         _ = await subscribe.next()
+
+        // Test if passing both nkey and nkeyPath throws an error
+        let badClient = NatsClientOptions()
+            .url(URL(string: natsServer.clientURL)!)
+            .nkeyFile(bundle.url(forResource: "nkey", withExtension: "")!)
+            .nkey("SUACH75SWCM5D2JMJM6EKLR2WDARVGZT4QC6LX3AGHSWOMVAKERABBBRWM")
+            .build()
+
+
+       var thrownError: Error?
+        do {
+            try await badClient.connect()
+        } catch {
+            thrownError = error
+        }
+
+        // Now assert that an error was thrown and check its type and properties
+        XCTAssertNotNil(thrownError, "Expected method to throw an error but it did not.")
+        if let natsError = thrownError as? NatsConfigError {
+            XCTAssertEqual(natsError.description, "cannot use both nkey and nkeyPath")
+        } else {
+            XCTFail("Unexpected error type: \(String(describing: thrownError))")
+        }
     }
 
     func testMutualTls() async throws {