Adding ability to post violations via middleware

[scalvert]

Adds support for combining the custom reporter with custom middleware, which allows for serializing the results to JSON.

// tests/test-helper.js
import { setupMiddlewareReporter } from 'ember-a11y-testing';
// ...

setupMiddlewareReporter();

// ...

This will setup a custom reporter, which gathers the test module name, test name, and violations for each failed audit. Once the suite is done, these results are posted to the testem middleware, ultimately serializing the results to disc.

TODO:

• Add tests for setupMiddlewareReporter
• Update setupMiddleware test to use real AxeResults
• Determine which specific directory path to pass to setupMiddlewareReporter in order to save the results.

[drewlee]

Just as a general question, since I didn't see this directly referred to in the code - how does the host application determine whether they want to run tests w/reporter vs no reporter (i.e., conditionally)? For example, we may not need the reporter for CI/CD process or local execution, while requiring the reporter for a nightly job. Would we just wrap setupMiddlewareReporter() in a conditional check in tests/test-helper.js?

[scalvert]

@drewlee - yes. I think we can configure that in the test-helper.js file via a custom query param.

[scalvert]

@rwjblue WDYT about us moving the parallel execution support (ember-exam) work to a subsequent PR? This will allow us to ship this increment, and be able to build out the subsequent supporting parts later.

[rwjblue]

The differences in these methods (from ember-cli's side) is very annoying 😭