Extracting html templates into a library (#16946)

* Extracting html templates into a library

* Moving tests to the right place

* Fixing tests

* Addressing PR review comments

* Addressing PR review comments

* Replacing attomic with RWMutex

* Returning errors as channel for Templates watcher

* Address PR review comments

* Other small fixes

* Simplifying NewWithWatcher

* Addressing PR review comments

* Making error handling on rendering templates more robust

* Fixing tests

* Changing how we return errors

* Fixing shadow variables

* Addressing PR review comments

* Logging errors from the outside of sendNotificationEmail

* Fixing lock in shutdown

* Fixing the resource copy for commands tests temporary directories

* Removing unused import

* A couple of tiny fixes

cmd/mattermost/commands/cmdtestlib.go

@@ -38,7 +38,7 @@ type testHelper struct {
 
 // Setup creates an instance of testHelper.
 func Setup(t testing.TB) *testHelper {
-	dir, err := ioutil.TempDir("", "testHelper")
+	dir, err := testlib.SetupTestResources()
 	if err != nil {
 		panic("failed to create temporary directory: " + err.Error())
 	}
@@ -60,7 +60,7 @@ func Setup(t testing.TB) *testHelper {
 
 // Setup creates an instance of testHelper.
 func SetupWithStoreMock(t testing.TB) *testHelper {
-	dir, err := ioutil.TempDir("", "testHelper")
+	dir, err := testlib.SetupTestResources()
 	if err != nil {
 		panic("failed to create temporary directory: " + err.Error())
 	}

cmd/mattermost/commands/config_flag_test.go

@@ -9,9 +9,6 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
-
-	"github.com/mattermost/mattermost-server/v5/utils"
-	"github.com/mattermost/mattermost-server/v5/utils/fileutils"
 )
 
 func TestConfigFlag(t *testing.T) {
@@ -19,16 +16,14 @@ func TestConfigFlag(t *testing.T) {
 	defer th.TearDown()
 	dir := th.TemporaryDirectory()
 
-	i18n, ok := fileutils.FindDir("i18n")
-	require.True(t, ok)
-	require.NoError(t, utils.CopyDir(i18n, filepath.Join(dir, "i18n")))
-
 	prevDir, err := os.Getwd()
 	require.NoError(t, err)
 	defer os.Chdir(prevDir)
 	os.Chdir(dir)
 
 	t.Run("version without a config file should fail", func(t *testing.T) {
+		err := os.RemoveAll("config")
+		require.NoError(t, err)
 		th.SetAutoConfig(false)
 		defer th.SetAutoConfig(true)
 		require.Error(t, th.RunCommand(t, "version"))