Establish a unique pattern for testing `UIViewController` presentation

See discussion here.

One options suggested is to use a mock:

let presenterMock = PresenterMockViewController()
...
presenter.presentReblog(blogService: blogService!, readerPost: readerPost!, origin: presenterMock)
...
presenterMock.expectPresentationToOccurr()

// In PresenterMockViewController
func expectPresentationToOccurr(file: ... = #file, line: ... = #line) {
  guard let presentExpectation = self.presentExpectation else { /* fail */ }

  waitForExpectations([presentExpectation], timeout: ...) { error in
    guard let error = error else { return }
    XCTFail("present was not called", file: file, line: line)
  }
}

Another option I used with good results in the past is the classic protocol-based test double. Something like:

protocol ViewControllerPresenting {

  // 1-1 copy of the UIViewController signature
  func present(_ viewControllerToPresent: UIViewController, animated flag: Bool, completion: (() -> Void)? = nil)
}

extension UIViewController: ViewControllerPresenting {}

class ViewControllerPresentingSpy {

  private(set) var presentedViewController: UIViewController?

  func present(_ viewControllerToPresent: UIViewController, animated flag: Bool, completion: (() -> Void)? = nil) {
    presentedViewController = viewControllerToPresent
    // doesn't actually present so we don't waste time nor need to worry about async
  }
}

// In tests
expect(presenterSpy.presentedViewController).toNot(beNil())

☝️ All those are just ideas to throw in the mix. We ought to have a look at what the existing tests do and what production code needs, and then choose an option that works best.

Tests to update

Anyone with contributor access can update this list by updating the PR description. Seems easier than adding comments to scroll through.

wordpress-mobile / WordPress-iOS

Establish a unique pattern for testing `UIViewController` presentation #19373

Tests to update