Stubs are not a part of traditional MVP, but they are used extensively in Tessell.

Stubs are “dummy” implementations of GWT widgets (e.g. TextBox has a StubTextBox) that provide close-enough-to-browser behavior for MVP/DOM-less unit tests.

By using a concrete implementation (the StubTextBox class), Tessell can provide this behavior in just one place (each stub) instead of an application’s unit tests each repeatedly setting up/verifying mock specifications for each widget behavior it uses in the test.

To do this, each IsXxx widget interface (see View Generation) has two implementations:

  1. A GwtXxx implementation. This is the real GWT widget, so uses GWT.*, DOM.*, etc. methods that only work in the browser or GWTTestCase.

  2. A StubXxx implementation. This is pure Java so can run in fast unit tests.

Tessell provides GwtXxx and StubXxx implementations out-of-the-box for most GWT widgets. For an example trio see: IsTextBox, GwtTextBox and StubTextBox.

Test Infrastructure For Free

Since Tessell is already generating the XxxView implementations for each ui.xml file in your project, it also generates a StubXxxView for testing.

The real XxxView will have @UiField-annotated fields of the real GWT widgets used at production time, just like you would code by hand, e.g.:

@UiField(provided = true)
final TextBox name = new org.tessell.widgets.GwtTextBox();

While the StubXxxView will simply instantiate the StubXxx version of each widget in the ui.xml file to use at test time, e.g.:

final StubTextBox name = new org.tessell.widgets.StubTextBox();

These “for free” StubXxxView classes make testing very easy to do–seeing the Tests page for examples.

How Dumb?

When you’re testing, the stub widgets attempt to mimic browser behavior, so you can do things like “press a key” or “type”:

public void testKeyPress() {
  view.nameTextBox().type("my name");

And the StubTextBox will, for press, fire key down, key press, and key up events and, for type, fire value change and blur events.

This behavior is generally “good enough” for 95% of the business logic you’re testing.

However, the stubs do not go out of their way to truly simulate a DOM-based browser. Nor do the stubs’ behavior correspond to any given browser implementation.

For example, if you set display:none on a parent stub widget, a child stub widget will still think it’s displayed–there is no cross-widget rendering/etc. logic as this rendering logic would be non-trivial (to write and to run, hence slowing down tests) and, for the far majority of the cases, it isn’t needed.

Stubs Are Great

For more on stubs, see: