Improve unit testing of Widgets

[kitsonk]

Enhancement

We need a good set of unit tests for a widget, that can be run against a virtual DOM (e.g. JSDOM) as well as a unit test in the native DOM without being a functional test. We should only use intended public APIs and generate the events/use synthetic events to drive the tests instead of relying upon driving functionality to provide full unit coverage of the widgets.

[matt-gadd]

As well as this, it might be nice to build into the harness higher level support for asserting v and w calls in an easy manner. At the moment our test assertions kind of straddle the middle ground of asserting VNodes which ideally we don't want to expose to the end user (given we have our own abstraction of a HNode).

If we assert against HNodes and WNodes we can do both shallow rendering (because both node types are lazy), as well as letting the user actually write v and w calls in the assertion block, which I think would be quite nice. For example something like:

const todos = [
    { id: 1, label: 'foo' },
    { id: 2, label: 'bar' }
];

const result = testWrapper(() => w(TodoList, { todos }));

assert.isTrue(result.equals(() => {
    return v('ul', { classes: { 'todo-list': true } }, [
        w(TodoItem, { key: 1, label: 'foo', completed: false }),
        w(TodoItem, { key: 2, label: 'bar', completed: false })
    ]);
}));

[kitsonk]

Good thoughts.

I guess though it needs to be permissive. For example if there are additional attributes, like event handlers, the harness won't have access to those references. So either only report missing values or allowing non-primitive equality for certain properties.

The thing too that we would want to avoid with something like that is people just copypasta their render function.

[matt-gadd]

Indeed. It would be similar to sinon's calledWith in that you only test the things that you pass explicitly (so they can be partial). So in this case you wouldn't assert against an event handler in the v call, you'd exercise the behaviour by triggering the event separately.

[rishson]

Is there overlap here with dojo/meta#131?

[kitsonk]

That is where the PR will be raised for this. We will reference back to this issue from that repo, but we haven't published @dojo/intern-helper yet, so dojo/meta#131 needs to stay open. We could in theory move this issue to dojo/intern-helper, but we can reference issues across repos.

[rishson]

👍 gotcha

[agubler]

@kitsonk can this be closed now given the test-extras and harness work?

[kitsonk]

Agreed.