Unit test case view controller crash swift

I am writing unit test cases for the view controllers in my iOS app. I am trying to test if the UI elements involving IBOutlets are not nil as in the code below.

class ClientsViewControllerTests: XCTestCase {

var clientsVC: ClientsTableViewController?

override func setUp() {
    super.setUp()

    let storyboard = UIStoryboard(name: "Clients", bundle: nil)

    clientsVC = storyboard.instantiateInitialViewController() as? ClientsTableViewController

    if let vc = clientsVC?{
        vc.loadView()
    }
}

override func tearDown() {

    super.tearDown()
    clientsVC = nil
}

func testClientViewControllerNotNil(){

    XCTAssertNotNil(clientsVC, "view controller cannot be nil")
}

I test fails and outputs "view controller cannot be nil"

I fail to understand why.However, the below test passes:

func testStoryBoard(){
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    var vc = storyboard.instantiateViewControllerWithIdentifier("MainVC") as UIViewController
    XCTAssertNotNil(vc,"Storyboard is not connected with a viewcontroller")

But I need to do it in the 1st method as I want to test for the IBOutlet bindings for the Specific viewController like:

XCAssertNotNil(vc.sendButton, "Send button is nil")

Kindly guide me why the test is failing and also how to test outlet binding and the action binding in ViewControllers