Testing framework for new pipeline

[timroes]

We should build a proper testing framework for the new pipeline. There are mainly two sort of tests, that should be able to be executed easily (currently I think Jest would be the go to way):

• Execute a pipeline and compare the returning data
• Execute a pipeline and render the output and compare the screenshot

After discussing that, we would like the pipeline to actually execute against a running Elasticsearch, to basically test the pipeline execution and chart rendering on a complete vertical stack.

Using utility functions tests should be really easy to write with the new framework:

import { pipelineData, pipelineRender } from '../pipeline_utils';

describe('esaggs function', () => {
  pipelineData('esaggs aggs="[{ type: count }]"').toEqual([ 421 ]);
  pipelineData('esaggs').toFail('missing param');
});

describe('pie chart', () => {
  pipelineRender('staticDemoData | pie_chart').toMatchScreenshot();
});

That way we could add new tests (e.g. for incoming bugs) in a very quick way. It's also very easy to have a huge amount of tests for different combinations (which it e.g. isn't currently for functional tests, since they need to click through all editors).

That framework would also then allow us to test the chart rendering decoupled from the data fetching. If we have an issue that a chart couldn't draw it's axis if the labels got too long, we don't need to find an aggregation configuration in the editor to draw that chart, but rather use demo data to directly produce the data we need in the pipeline and just test the actual chart rendering. The same vice versa for issues purely in the data fetching part of the pipeline.