[TESTS] coverage for SignInOAuthCallback

(cherry picked from commit f8e1619b99)
(cherry picked from commit 46d8bc9bdf)
(cherry picked from commit e0c7b7055f)
(cherry picked from commit faab747f8e)
(cherry picked from commit 46acb6a9a7)
(cherry picked from commit 22d964e744)
(cherry picked from commit 4c8a6031ac)

tests/integration/integration_test.go

@@ -39,6 +39,8 @@ import (
 	"code.gitea.io/gitea/tests"
 
 	"github.com/PuerkitoBio/goquery"
+	"github.com/markbates/goth"
+	"github.com/markbates/goth/gothic"
 	goth_gitlab "github.com/markbates/goth/providers/gitlab"
 	"github.com/stretchr/testify/assert"
 	"github.com/xeipuuv/gojsonschema"
@@ -232,6 +234,14 @@ func getUserToken(t testing.TB, userName string, scope ...auth.AccessTokenScope)
 	return getTokenForLoggedInUser(t, loginUser(t, userName), scope...)
 }
 
+func mockCompleteUserAuth(mock func(res http.ResponseWriter, req *http.Request) (goth.User, error)) func() {
+	old := gothic.CompleteUserAuth
+	gothic.CompleteUserAuth = mock
+	return func() {
+		gothic.CompleteUserAuth = old
+	}
+}
+
 func addAuthSource(t *testing.T, payload map[string]string) *auth.Source {
 	session := loginUser(t, "user1")
 	payload["_csrf"] = GetCSRF(t, session, "/admin/auths/new")