Add tests to model/notificationevent

[kentakozuka]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[ffjlabo]

Let's add t.Parallel 👍

[ffjlabo]

it should be better to add t.Parallel and assign a value as tt := tt 👀

Suggested change

	for _, tt := range tests {
	t.Run(tt.name, func(t *testing.T) {
	e := NotificationEvent{Type: tt.typ}
	got := e.Group()
	assert.Equal(t, tt.want, got)
	})
	for _, tt := range tests {
	tt := tt
	t.Run(tt.name, func(t *testing.T) {
	t.Parallel()
	e := NotificationEvent{Type: tt.typ}
	got := e.Group()
	assert.Equal(t, tt.want, got)
	})

[kentakozuka]

@ffjlabo Fixed 👍

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (743bd9e) 30.55% compared to head (4c69e15) 30.61%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4631      +/-   ##
==========================================
+ Coverage   30.55%   30.61%   +0.06%     
==========================================
  Files         221      221              
  Lines       25937    25937              
==========================================
+ Hits         7925     7941      +16     
+ Misses      17363    17348      -15     
+ Partials      649      648       -1     

see 2 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[ffjlabo]

Thank you for adding test!!