Adding changes to separate unit tests and integration tests (#13670)

* Introducing unit (not integration) tests for the app layer

* Initial support for unit tests at the API

* Adding unit tests support to the store layer

* Add unit tests support in commands

* Adding last tests needed for run unit tests properly

* Fixing govet

* Removing some duplication

* Fixing tests

* Fixing tests

* Not compiling test helpers with the main module for api

* Revert "Not compiling test helpers with the main module for api"

This reverts commit 36a199bbe0f7503f665f5d6c7b41c53aabc2e54f.

* Fixing tests

* Fixing unit tests

* More consistency between api4/apiteslib.go and app/helper_test.go

* Renaming things to make more obvious the new Setup functions purpose

* Reverting change in go.sum

* Start with empty mock for app layer

* Start with empty mock for api layer

* Start with empty mock for web layer

* Renaming SetupWithStoreMockConfig to SetupConfigWithStoreMock

* Fixing tests on web package

* Removing unnecesary function

app/notification_push_test.go

@@ -8,8 +8,10 @@ import (
 	"testing"
 
 	"github.com/mattermost/mattermost-server/v5/model"
+	"github.com/mattermost/mattermost-server/v5/store/storetest/mocks"
 	"github.com/mattermost/mattermost-server/v5/utils"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
 	"github.com/stretchr/testify/require"
 )
 
@@ -539,9 +541,20 @@ func TestDoesStatusAllowPushNotification(t *testing.T) {
 }
 
 func TestGetPushNotificationMessage(t *testing.T) {
-	th := Setup(t)
+	th := SetupWithStoreMock(t)
 	defer th.TearDown()
 
+	mockStore := th.App.Srv().Store.(*mocks.Store)
+	mockUserStore := mocks.UserStore{}
+	mockUserStore.On("Count", mock.Anything).Return(int64(10), nil)
+	mockPostStore := mocks.PostStore{}
+	mockPostStore.On("GetMaxPostSize").Return(65535, nil)
+	mockSystemStore := mocks.SystemStore{}
+	mockSystemStore.On("GetByName", "InstallationDate").Return(&model.System{Name: "InstallationDate", Value: "10"}, nil)
+	mockStore.On("User").Return(&mockUserStore)
+	mockStore.On("Post").Return(&mockPostStore)
+	mockStore.On("System").Return(&mockSystemStore)
+
 	for name, tc := range map[string]struct {
 		Message                  string
 		explicitMention          bool