[MM-62408] Server Code Coverage with Fully Parallel Tests (#30078)

* TestPool

* Store infra

* Store tests updates

* Bump maximum concurrent postgres connections

* More infra

* channels/jobs

* channels/app

* channels/api4

* Protect i18n from concurrent access

* Replace some use of os.Setenv

* Remove debug

* Lint fixes

* Fix more linting

* Fix test

* Remove use of Setenv in drafts tests

* Fix flaky TestWebHubCloseConnOnDBFail

* Fix merge

* [MM-62408] Add CI job to generate test coverage (#30284)

* Add CI job to generate test coverage

* Remove use of Setenv in drafts tests

* Fix flaky TestWebHubCloseConnOnDBFail

* Fix more Setenv usage

* Fix more potential flakyness

* Remove parallelism from flaky test

* Remove conflicting env var

* Fix

* Disable parallelism

* Test atomic covermode

* Disable parallelism

* Enable parallelism

* Add upload coverage step

* Fix codecov.yml

* Add codecov.yml

* Remove redundant workspace field

* Add Parallel() util methods and refactor

* Fix formatting

* More formatting fixes

* Fix reporting

server/channels/store/sqlstore/main_test.go

@@ -4,8 +4,12 @@
 package sqlstore_test
 
 import (
+	"flag"
+	"os"
+	"strconv"
 	"testing"
 
+	"github.com/mattermost/mattermost/server/public/shared/mlog"
 	"github.com/mattermost/mattermost/server/v8/channels/store/sqlstore"
 	"github.com/mattermost/mattermost/server/v8/channels/testlib"
 )
@@ -13,10 +17,21 @@ import (
 var mainHelper *testlib.MainHelper
 
 func TestMain(m *testing.M) {
+	var parallelism int
+	if f := flag.Lookup("test.parallel"); f != nil {
+		parallelism, _ = strconv.Atoi(f.Value.String())
+	}
+	runParallel := os.Getenv("ENABLE_FULLY_PARALLEL_TESTS") == "true" && parallelism > 1
+	if runParallel {
+		mlog.Info("Fully parallel tests enabled", mlog.Int("parallelism", parallelism))
+	} else {
+		parallelism = 1
+	}
+
 	mainHelper = testlib.NewMainHelperWithOptions(nil)
 	defer mainHelper.Close()
 
-	sqlstore.InitTest(mainHelper.Logger)
+	sqlstore.InitTest(mainHelper.Logger, parallelism)
 
 	mainHelper.Main(m)
 	sqlstore.TearDownTest()