[WIP] Use custom summary trend stat

[asettouf]

Hello,

I started working on #1611 and though I think I figured it out, however my solution is the ugliest thing I've done in a long while...

Do note that I'm relatively recent at coding in Go.

Any suggestion would be highly appreciated!

[na--]

Ah, sorry, I should have been more clear in #1611 (comment), and removed the good first issue label 😞 Thanks for making this PR, however, we're currently in the middle of a big revamping in how the end-of-test summary is handled, so unfortunately I can't merge this...

I should have created a new issue after our internal discussions, and closed (or commented in) the old ones... And I am hoping to make a PR in the next few days with the changes, so it's probably a bit late now. But to give you a summary, we're trying to address a whole bunch of current issues simultaneously (#351, #647, #1319, #1611, #1675, #1120, #1366, #1316) and lay the groundwork for some future improvements as well (#1315, maybe #817).

We'll do that by allowing users to define a JS function for handling the end-of-test summary in a very flexible way. Something like this:

import http from 'k6/http';
import { JUnit, TextSummary } from 'https://jslib.k6.io/k6-summary/1.0.0/index.js' // or something like that
// ...
export function handleSummary(data) {
    // only show the human-readable intermediate summary if the test is still running
    if (data.execution.runStatus == 'running') {
        return {stdout: TextSummary(data.summary)};
    }
   
    // save everything to files and send it to a server when the test finishes or gets aborted
    http.post('https://example.com/testResults', JSON.stringify(data));

    return {
        'stdout': TextSummary(data.summary),
        './results/junit.xml': JUnit(data.summary),
        './results/summary.json': JSON.stringify(data.summary),
    }
}

[asettouf]

@na-- All right fair enough, that makes more sense than what I was trying to do yesterday! :)