Fix /msg switching teams (#7753)

* Fix /msg switching teams

* simplify a bit

app/command_msg_test.go

@@ -0,0 +1,31 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import (
+	"testing"
+
+	"github.com/nicksnyder/go-i18n/i18n"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/mattermost/mattermost-server/model"
+)
+
+func TestMsgProvider(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+
+	team := th.CreateTeam()
+	th.LinkUserToTeam(th.BasicUser, team)
+	cmd := &msgProvider{}
+	resp := cmd.DoCommand(th.App, &model.CommandArgs{
+		T:       i18n.IdentityTfunc(),
+		SiteURL: "http://test.url",
+		TeamId:  team.Id,
+		UserId:  th.BasicUser.Id,
+	}, "@"+th.BasicUser2.Username+" hello")
+	channelName := model.GetDMNameFromIds(th.BasicUser.Id, th.BasicUser2.Id)
+	assert.Equal(t, "", resp.Text)
+	assert.Equal(t, "http://test.url/"+team.Name+"/channels/"+channelName, resp.GotoLocation)
+}