PLT-3131 Add slash command for sending email invites (#3218)

* Add slash command for sending email invites

* Add response for empty message and trim commas

* Check for @ in email addresses before sending

* Update invite people error message

api/command_invite_people_test.go

@@ -0,0 +1,31 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package api
+
+import (
+	"testing"
+
+	"github.com/mattermost/platform/model"
+)
+
+func TestInvitePeopleCommand(t *testing.T) {
+	th := Setup().InitBasic()
+	Client := th.BasicClient
+	channel := th.BasicChannel
+
+	r1 := Client.Must(Client.Command(channel.Id, "/invite_people test@example.com", false)).Data.(*model.CommandResponse)
+	if r1 == nil {
+		t.Fatal("Command failed to execute")
+	}
+
+	r2 := Client.Must(Client.Command(channel.Id, "/invite_people test1@example.com test2@example.com", false)).Data.(*model.CommandResponse)
+	if r2 == nil {
+		t.Fatal("Command failed to execute")
+	}
+
+	r3 := Client.Must(Client.Command(channel.Id, "/invite_people", false)).Data.(*model.CommandResponse)
+	if r3 == nil {
+		t.Fatal("Command failed to execute")
+	}
+}