[MM-9904] Add /invite slash command to invite users to a channel (#8482)

* [MM-9904] Add /invite slash command to invite users to a channel

* Update en.json

app/command_invite_test.go

@@ -0,0 +1,108 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/mattermost/mattermost-server/model"
+)
+
+func TestInviteProvider(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+
+	channel := th.createChannel(th.BasicTeam, model.CHANNEL_OPEN)
+	privateChannel := th.createChannel(th.BasicTeam, model.CHANNEL_PRIVATE)
+	dmChannel := th.CreateDmChannel(th.BasicUser2)
+
+	basicUser3 := th.CreateUser()
+	th.LinkUserToTeam(basicUser3, th.BasicTeam)
+	basicUser4 := th.CreateUser()
+
+	InviteP := InviteProvider{}
+	args := &model.CommandArgs{
+		T:         func(s string, args ...interface{}) string { return s },
+		ChannelId: th.BasicChannel.Id,
+		TeamId:    th.BasicTeam.Id,
+		Session:   model.Session{UserId: th.BasicUser.Id, TeamMembers: []*model.TeamMember{{TeamId: th.BasicTeam.Id, Roles: model.TEAM_USER_ROLE_ID}}},
+	}
+
+	userAndWrongChannel := "@" + th.BasicUser2.Username + " wrongchannel1"
+	userAndChannel := "@" + th.BasicUser2.Username + " ~" + channel.Name + " "
+	userAndDisplayChannel := "@" + th.BasicUser2.Username + " ~" + channel.DisplayName + " "
+	userAndPrivateChannel := "@" + th.BasicUser2.Username + " ~" + privateChannel.Name
+	userAndDMChannel := "@" + basicUser3.Username + " ~" + dmChannel.Name
+
+	tests := []struct {
+		desc     string
+		expected string
+		msg      string
+	}{
+		{
+			desc:     "Missing user and channel in the command",
+			expected: "api.command_invite.missing_message.app_error",
+			msg:      "",
+		},
+		{
+			desc:     "User added in the current channel",
+			expected: "",
+			msg:      th.BasicUser2.Username,
+		},
+		{
+			desc:     "Add user to another channel not the current",
+			expected: "api.command_invite.success",
+			msg:      userAndChannel,
+		},
+		{
+			desc:     "try to add a user to a direct channel",
+			expected: "api.command_invite.directchannel.app_error",
+			msg:      userAndDMChannel,
+		},
+		{
+			desc:     "Try to add a user to a invalid channel",
+			expected: "api.command_invite.channel.error",
+			msg:      userAndWrongChannel,
+		},
+		{
+			desc:     "Try to add a user to an private channel",
+			expected: "api.command_invite.success",
+			msg:      userAndPrivateChannel,
+		},
+		{
+			desc:     "Using display channel name which is different form Channel name",
+			expected: "api.command_invite.channel.error",
+			msg:      userAndDisplayChannel,
+		},
+		{
+			desc:     "Invalid user to current channel",
+			expected: "api.command_invite.missing_user.app_error",
+			msg:      "@invalidUser123",
+		},
+		{
+			desc:     "Invalid user to current channel without @",
+			expected: "api.command_invite.missing_user.app_error",
+			msg:      "invalidUser321",
+		},
+		{
+			desc:     "try to add a user which is not part of the team",
+			expected: "api.command_invite.fail.app_error",
+			msg:      basicUser4.Username,
+		},
+		{
+			desc:     "try to add a user to a direct channel",
+			expected: "api.command_invite.directchannel.app_error",
+			msg:      userAndDMChannel,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
+			actual := InviteP.DoCommand(th.App, args, test.msg).Text
+			assert.Equal(t, test.expected, actual)
+		})
+	}
+}