Tool of Thought

APL for the Practical Man

Testing GUIs

August 14, 2023

I'm currently in the process of extracting a GUI testing framework from a private project and adding it to Provanto. Writing automated GUI tests for ⎕WC applications is somewhat of a dark art. Nowhere is the principle of Test Driven Development (TDD) more important than with GUI programming and ⎕WC. Writing GUI code without forethought will invariably yield code that is simply untestable. Of course we don't have forethought until we have written a bunch of GUI code first, and then attempted to write test code, so we are generally doomed to have untestable GUI code that must be rewritten.

Future posts will explore the underlying framework code in detail. Here we just take a look at the overall basics, what a test function looks like, and how to write one. Once the dark art is mastered and buried in the framework, and we learn how to write testable GUI apps, the tests themselves are clean, neat, and simple to write, read, and maintain.

Testing a GUI starts with a reference to the primary form object of an application. The Init function takes this form, instantiates a few properties in it, and then injects a few functions back into the test namespace:

     t.Keys←KeySpace 0
     _←⍵ Fix¨API 0

In addition to Assert and Try (the functions that Provanto injects into the test space), we now will have two more reserved words: Enter and Get. Both of these functions are bound with the reference to the form, so it is not needed as an argument.

The Init function may be called in the Startup function for a suite of tests, or directly in a test function.

Provanto includes a sample GUI application and a few tests to show how it is done. A typical GUI test fires events on objects, then inspects the state of the GUI and the application and makes assertions. Let's take a look at one:

     s←GetAppState 0
     Enter'Name' 'A12B345C':
     Assert e.Text≡'ABC':
     Assert s.AllowDigits:
     Enter'Name' '12345':
     Assert e.Text≡'ABC12345':

This function assumes that Init has already been called. GetAppState is an application specific helper function that returns a namespace with a few variables representing the state of the application. Of course in a real application, the application state may be represented by a complex object model, or a folder on disk, or both and more.

The Get function takes the name of a GUI object and returns a reference to it, providing access to the state of the GUI.

The Enter function allows us to fire events at the GUI. To click on a push button or menu item, or to change the state of a radio button or check box, we simply call the Enter function with the name of the object. To enter text in an edit box, we call Enter with both the name of the object and the text to enter.

We can also fire specific events. For example, to double click on the Name edit object:

Enter 'Name' (⊂'MouseDblClick')

A full event message may be provided as well:

Enter 'Name' ('KeyPress' 'RC' 0 39 0) 

KeyPress events are very common, so a namespace with KeyPress events is provided, to make it easy to fire specific keys on objects:

Enter 'Name' Keys.RightCursor  

The above test is implement as a dfn, and thus naked guards are necessary to prevent the function from exiting on the lines that lack an assignment, specifically the lines calling Enter. We could of course assign a useless result instead, but it adds a lot of clutter. The naked guard is already used on the lines making assertions, so it's not that much of stretch, but some might find it objectionable. I'm not entirely sure how I feel about it. A trad function works just as well, arguably cleaner if there are not too many local variables:

 z←TestAllowDigitsProperty x;s;e
 s←GetAppState 0
 Enter'Name' 'A12B345C'
 Assert e.Text≡'ABC'
 Assert s.AllowDigits
 Enter'Name' '12345'
 Assert e.Text≡'ABC12345'

The main point is that both of these functions, the dfn and trad fn, have little to no extraneous code. The functions are easy to write and read. The two API functions Enter and Get provide almost all that is needed. The test functions are also easy to trace, and you can see exactly what the GUI is doing while stepping through them.