[#1522] adm/helper: Unexport GetFrostfsIDAdmin()

It is used in `helper` package only, besides unit-tests.
Move unit-tests to the same package, where they belong.

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

cmd/frostfs-adm/internal/modules/morph/helper/frostfsid_test.go

@@ -0,0 +1,53 @@
+package helper
+
+import (
+	"encoding/hex"
+	"testing"
+
+	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
+	"github.com/nspcc-dev/neo-go/pkg/encoding/address"
+	"github.com/spf13/viper"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFrostfsIDConfig(t *testing.T) {
+	pks := make([]*keys.PrivateKey, 4)
+	for i := range pks {
+		pk, err := keys.NewPrivateKey()
+		require.NoError(t, err)
+		pks[i] = pk
+	}
+
+	fmts := []string{
+		pks[0].GetScriptHash().StringLE(),
+		address.Uint160ToString(pks[1].GetScriptHash()),
+		hex.EncodeToString(pks[2].PublicKey().UncompressedBytes()),
+		hex.EncodeToString(pks[3].PublicKey().Bytes()),
+	}
+
+	for i := range fmts {
+		v := viper.New()
+		v.Set("frostfsid.admin", fmts[i])
+
+		actual, found, err := getFrostfsIDAdmin(v)
+		require.NoError(t, err)
+		require.True(t, found)
+		require.Equal(t, pks[i].GetScriptHash(), actual)
+	}
+
+	t.Run("bad key", func(t *testing.T) {
+		v := viper.New()
+		v.Set("frostfsid.admin", "abc")
+
+		_, found, err := getFrostfsIDAdmin(v)
+		require.Error(t, err)
+		require.True(t, found)
+	})
+	t.Run("missing key", func(t *testing.T) {
+		v := viper.New()
+
+		_, found, err := getFrostfsIDAdmin(v)
+		require.NoError(t, err)
+		require.False(t, found)
+	})
+}