I have been trying to write test cases in Swift to test my ViewController. However, when I try to instantiate my own ViewController in a XCTestCase I get \"Use of undecla
You should add ViewController.swift file's target membership also as your test target also if you are not using framework. Select class file add to target as shown in image:

OR
If you are ViewController is within a framework : ViewController class is in different target and You are not declaring class with public access level. By default Classes are internal (Accessible within a target). Declare it as public and also make methods or properties as public if you want to access it i.e
public class ViewController: UIViewController {
public var content: String!
override public func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
override public func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
In your test target, just import the module you want to test using the @testable keyword:
@testable import moduleToTest
You can now access public and internal symbols in your test target.
swift 2 Xcode 7 unit testing