Move more issue assignee code from models to issue service (#8690)

* Move more issue assignee code from models to issue service

* fix test

services/issue/assignee_test.go

@@ -0,0 +1,37 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package issue
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDeleteNotPassedAssignee(t *testing.T) {
+	assert.NoError(t, models.PrepareTestDatabase())
+
+	// Fake issue with assignees
+	issue, err := models.GetIssueWithAttrsByID(1)
+	assert.NoError(t, err)
+
+	user1, err := models.GetUserByID(1) // This user is already assigned (see the definition in fixtures), so running  UpdateAssignee should unassign him
+	assert.NoError(t, err)
+
+	// Check if he got removed
+	isAssigned, err := models.IsUserAssignedToIssue(issue, user1)
+	assert.NoError(t, err)
+	assert.True(t, isAssigned)
+
+	// Clean everyone
+	err = DeleteNotPassedAssignee(issue, user1, []*models.User{})
+	assert.NoError(t, err)
+
+	// Check they're gone
+	assignees, err := models.GetAssigneesByIssue(issue)
+	assert.NoError(t, err)
+	assert.Equal(t, 0, len(assignees))
+}