Add ability to mock meta providers

[kitsonk]

Type: feature

The following has been addressed in the PR:

• There is a related issue
• All code matches the style guide
• Unit or Functional tests are included in the PR

Description:

This PR provides the ability to mock meta providers.

Allows for mocking of meta providers when testing a widget. The method .mockMeta() takes two arguments, first the meta provider class and the second argument being a map of methods to mock on the provider when the harness widget is created.

For example, to provide mocked Dimensions for a widget:

const widget = harness.widget(MyWidget);

const rootDimensions = {
    offset: { height: 100, left: 100, top: 100, width: 100 },
    position: { bottom: 200, left: 100, right: 200, top: 100 },
    scroll: { height: 100, left: 100, top: 100, width: 100 },
    size: { width: 100, height: 100 }
};
const emptyDimensions = {
    offset: { height: 0, left: 0, top: 0, width: 0 },
    position: { bottom: 0, left: 0, right: 0, top: 0 },
    scroll: { height: 0, left: 0, top: 0, width: 0 },
    size: { width: 0, height: 0 }
};

const handle = widget.mockMeta(Dimensions, {
    get(key: string | number) {
        return key === 'root' ? rootDimensions : emptyDimensions;
    }
});

The handle returned from the .mockMeta function can be used to remove the mocks.

To facilitate usage under TypeScript, there is a special context type (MetaMockContext) that is exported from the harness module. This is designed to represent the run-time context of the mock methods, which will allow access to this.invalidate() and this.getNode() which may be required to create an appropriate mock.

For example, to invalidate a widget via the meta provider mock:

import harness, { MetaMockContext } from '@dojo/text-extras/harness';

const widget = harness.widget(MyWidget);

widget.mockMeta(Dimensions, {
    get(this: MetaMockContext<Dimensions>, key: string | number) {
        this.invalidate();
        return {}
    }
})

Resolves #65

[codecov]

Codecov Report

Merging #68 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #68      +/-   ##
==========================================
+ Coverage   99.05%   99.08%   +0.02%     
==========================================
  Files          10       10              
  Lines         637      653      +16     
  Branches      158      160       +2     
==========================================
+ Hits          631      647      +16     
  Partials        6        6

Impacted Files	Coverage Δ
src/harness.ts	97.83% <100%> (+0.2%)	⬆️

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[bitpshr]

I like the resulting API.

[bitpshr]

Why does this have to be explicitly marked as public?

[kitsonk]

It is unnecessary, though we have been trying to be more explicit in the visibility operators. I can remove it if it is a concern. I forgot I did it.

[smhigley]

The API looks good. This will make Listbox tests much prettier :)