alertmanager: adds tests for should notify

pkg/services/alerting/notifiers/alertmanager_test.go

 package notifiers
 
 import (
+	"context"
 	"testing"
 
 	"github.com/grafana/grafana/pkg/components/simplejson"
+	"github.com/grafana/grafana/pkg/log"
 	m "github.com/grafana/grafana/pkg/models"
+	"github.com/grafana/grafana/pkg/services/alerting"
 	. "github.com/smartystreets/goconvey/convey"
 )
 
+func TestWhenAlertManagerShouldNotify(t *testing.T) {
+	tcs := []struct {
+		prevState m.AlertStateType
+		newState  m.AlertStateType
+
+		expect bool
+	}{
+		{
+			prevState: m.AlertStatePending,
+			newState:  m.AlertStateOK,
+			expect:    false,
+		},
+		{
+			prevState: m.AlertStateAlerting,
+			newState:  m.AlertStateOK,
+			expect:    true,
+		},
+		{
+			prevState: m.AlertStateOK,
+			newState:  m.AlertStatePending,
+			expect:    false,
+		},
+		{
+			prevState: m.AlertStateUnknown,
+			newState:  m.AlertStatePending,
+			expect:    false,
+		},
+	}
+
+	for _, tc := range tcs {
+		am := &AlertmanagerNotifier{log: log.New("test.logger")}
+		evalContext := alerting.NewEvalContext(context.TODO(), &alerting.Rule{
+			State: tc.prevState,
+		})
+
+		evalContext.Rule.State = tc.newState
+
+		res := am.ShouldNotify(context.TODO(), evalContext, &m.AlertNotificationState{})
+		if res != tc.expect {
+			t.Errorf("got %v expected %v", res, tc.expect)
+		}
+	}
+}
+
 func TestAlertmanagerNotifier(t *testing.T) {
 	Convey("Alertmanager notifier tests", t, func() {