Add timestamps for logs into the functional tests reports (elastic#24509

)

* feat(NA): first version to add logs to the functional test runner when running on dev.

* fix(NA): change timestamp position.

* test(NA): add unit test for tooling log text writer with timestamp.

* test(NA): update test and snapshots

* fix(NA): only apply timestamp logs for the jenkins test reports.

* test(NA): update jest snapshots correctly.

* fix(NA): only add timestamp for the test results cached chunk logs.

* fix(NA): rollback bad changes.

* refact(NA): change comments on code to be more clear with the purpose.

* refact(NA): rename chunk to line.

* feat(NA): log the relative time info since the start time of the task instead of the absolute time.

src/functional_test_runner/lib/mocha/reporter/reporter.js

@@ -21,6 +21,7 @@ import { format } from 'util';
 
 import Mocha from 'mocha';
 import { ToolingLogTextWriter } from '@kbn/dev-utils';
+import moment from 'moment';
 
 import { setupJUnitReportGeneration } from '../../../../dev';
 import * as colors from './colors';
@@ -33,6 +34,7 @@ export function MochaReporterProvider({ getService }) {
   const log = getService('log');
   const config = getService('config');
   let originalLogWriters;
+  let reporterCaptureStartTime;
 
   return class MochaReporter extends Mocha.reporters.Base {
     constructor(runner, options) {
@@ -60,7 +62,10 @@ export function MochaReporterProvider({ getService }) {
     onStart = () => {
       if (config.get('mochaReporter.captureLogOutput')) {
         log.warning('debug logs are being captured, only error logs will be written to the console');
+
+        reporterCaptureStartTime = moment();
         originalLogWriters = log.getWriters();
+
         log.setWriters([
           new ToolingLogTextWriter({
             level: 'error',
@@ -69,7 +74,7 @@ export function MochaReporterProvider({ getService }) {
           new ToolingLogTextWriter({
             level: 'debug',
             writeTo: {
-              write: (chunk) => {
+              write: (line) => {
                 // if the current runnable is a beforeEach hook then
                 // `runner.suite` is set to the suite that defined the
                 // hook, rather than the suite executing, so instead we
@@ -80,7 +85,14 @@ export function MochaReporterProvider({ getService }) {
                   ? this.runner.test.parent
                   : this.runner.suite;
 
-                recordLog(currentSuite, chunk);
+                // We are computing the difference between the time when this
+                // reporter has started and the time when each line are being
+                // logged in order to be able to label the test results log lines
+                // with this relative time information
+                const diffTimeSinceStart = moment().diff(reporterCaptureStartTime);
+                const readableDiffTimeSinceStart = `[${moment(diffTimeSinceStart).format('HH:mm:ss')}] `;
+
+                recordLog(currentSuite, `${readableDiffTimeSinceStart} ${line}`);
               }
             }
           })