Testables

Make private properties testable.

Background

Let's assume that there is a class named ProfileViewController. This class has a property username which sets usernameLabel.text when the new value is assigned. Unfortunately, we cannot write an unit test because usernameLabel is a private property.

ProfileViewController.swift

class ProfileViewController {
  var username: String? {
    didSet {
      self.usernameLabel.text = self.username
    }
  }
  private let usernameLabel = UILabel()
}

ProfileViewControllerTests.swift

// when
viewController.username = "devxoul"

// then
let usernameLabel = viewController.usernameLabel // 🚫 private
XCTAssertEqual(usernameLabel.text, "devxoul")

Solution

Testables provides a generic way to expose private properties using Swift KeyPath.

Add the lines below to ProfileViewController.swift:

#if DEBUG
import Testables

extension ProfileViewController: Testable {
  final class TestableKeys: TestableKey<Self> {
    let usernameLabel = \Self.usernameLabel
  }
}
#endif

And update the test code:

// when
viewController.username = "devxoul"

// then
let usernameLabel = viewController.testables[\.usernameLabel] // ✅
XCTAssertEqual(usernameLabel.text, "devxoul")

License

Testables is under MIT license. See the LICENSE file for more info.