[MM-43917] Cloud Freemium limits API: messages/posts (#20152)

* WIP - Add api and app funcs

* Add test cases

* Add utils testcases

* Exclude deleted posts

* Add doc for func

* Move api from cloud to usage

* Allow api access to authenticated users

* Change int to int64

* Fix lint issue

* Simplify err check

Co-authored-by: Ashish Bhate <ashish.bhate@mattermost.com>

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Ashish Bhate <ashish.bhate@mattermost.com>

api4/usage_test.go

@@ -0,0 +1,39 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package api4
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetPostsUsage(t *testing.T) {
+	t.Run("unauthenticated users can not access", func(t *testing.T) {
+		th := Setup(t)
+		defer th.TearDown()
+
+		th.Client.Logout()
+
+		usage, r, err := th.Client.GetPostsUsage()
+		assert.Error(t, err)
+		assert.Nil(t, usage)
+		assert.Equal(t, http.StatusUnauthorized, r.StatusCode)
+	})
+
+	t.Run("good request returns response", func(t *testing.T) {
+		// Following calls create a total of 15 posts
+		th := Setup(t).InitBasic()
+		defer th.TearDown()
+		th.CreatePost()
+		th.CreatePost()
+
+		usage, r, err := th.Client.GetPostsUsage()
+		assert.NoError(t, err)
+		assert.Equal(t, http.StatusOK, r.StatusCode)
+		assert.NotNil(t, usage)
+		assert.Equal(t, int64(10), usage.Count)
+	})
+}