[#29] Add type to metrics description

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

metrics/desc_test.go

@@ -8,17 +8,28 @@ import (
 	"os"
 	"testing"
 
+	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/pool"
 	"github.com/stretchr/testify/require"
 )
 
+type mock struct{}
+
+func (m mock) Statistic() pool.Statistic {
+	return pool.Statistic{}
+}
+
 var metricsPath = flag.String("out", "", "File to export http gateway metrics to.")
 
 func TestDescribeAll(t *testing.T) {
+	// to check correct metrics type mapping
+	_ = NewGateMetrics(mock{})
+
 	flag.Parse()
 
 	require.NotEmpty(t, metricsPath, "flag 'out' must be provided to dump metrics description")
 
-	data, err := json.Marshal(DescribeAll())
+	desc := DescribeAll()
+	data, err := json.Marshal(desc)
 	require.NoError(t, err)
 
 	err = os.WriteFile(*metricsPath, data, 0644)