MM-18384 - Migrate tests from "app/notification_test.go" to use testify (#13526)

* MM-18384 - Migrate tests from "app/notification_test.go" to use testify

* fix golangcibot

* fix golangcibot

* break complex comparisons into multiple simple statements

* make test cleaner

* add missing changes

go.sum

@@ -252,6 +252,7 @@ github.com/mattermost/gosaml2 v0.3.2 h1:kq2dY5qUe6fPPHra171GVlgo+ycBsEog0gZMetxL
 github.com/mattermost/gosaml2 v0.3.2/go.mod h1:Z429EIOiEi9kbq6yHoApfzlcXpa6dzRDc6pO+Vy2Ksk=
 github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d h1:2DV7VIlEv6J5R5o6tUcb3ZMKJYeeZuWZL7Rv1m23TgQ=
 github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d/go.mod h1:HLbgMEI5K131jpxGazJ97AxfPDt31osq36YS1oxFQPQ=
+github.com/mattermost/ldap v3.0.4+incompatible h1:SOeNnz+JNR+foQ3yHkYqijb9MLPhXN2BZP/PdX23VDU=
 github.com/mattermost/rsc v0.0.0-20160330161541-bbaefb05eaa0 h1:G9tL6JXRBMzjuD1kkBtcnd42kUiT6QDwxfFYu7adM6o=
 github.com/mattermost/rsc v0.0.0-20160330161541-bbaefb05eaa0/go.mod h1:nV5bfVpT//+B1RPD2JvRnxbkLmJEYXmRaaVl15fsXjs=
 github.com/mattermost/viper v1.0.4 h1:cMYOz4PhguscGSPxrSokUtib5HrG4gCpiUh27wyA3d0=