Fixes #111

This reverts #109 and subsequently will impact this issue: #107.

As of Toaster 2.0.4 Toast.finish() skips setting isFinished=true and isExecuting=false when the operation is not executing. This causes an issue where calling cancel() right after show() will cause the operation queue to stall.

On the same vibe, since ToastCenter.currentToast didn't exclude cancelled and finished tasks, calling cancel() right after show() would cause currentToast to not be nil.

What's the bug

let toast = Toast(text: "text").show()
toast.cancel()

Since show() adds the operation to a background queue, it means Toast.start actually postpones the start() which causes cancel() to be called before start().

According to the cancel() docs:

You must change the value returned by isFinished to true and the value returned by isExecuting to false. You must make these changes even if the operation was cancelled before it started executing.

So cancel() needs to set isFinished=true and isExecuting=false. However in #109 we added a check that would prevent setting those flags if the operation is not executing. Since we're not setting those flags properly, the operation queue will call start() and wait for the operation to complete. However the operation will never complete because we ignore the start call if the operation is cancelled (see below).

Furthermore, according to start()'s documentation, we need to ignore finished/executing/cancelled operations because we're overriding the default implementation of start() which was performing those checks for us:

This method also performs several checks to ensure that the operation can actually run. For example, if the receiver was cancelled or is already finished, this method simply returns without calling main().

The fix

• Removed the isExecuting guard in Toast.finish()

• Removed a super.start() call since the docs specify that it must not be called

  Your custom implementation must not call super at any time`

  Instead, we're calling main() from start() directly.

• Since ToastCenter.currentToast would return finished/cancelled operations, I fixed it by filtering those out

• Added basic unit tests to make sure those issues are fixed, as well as one basic test that introspects the shared window.

Let me know if you have any question!