client statVFS: normalize the returned error

added a test case for the request server to check os.IsNotExist error

client.go

@@ -638,7 +638,7 @@ func (c *Client) StatVFS(path string) (*StatVFS, error) {
 
 	// the resquest failed
 	case sshFxpStatus:
-		return nil, errors.New(fxp(sshFxpStatus).String())
+		return nil, normaliseError(unmarshalStatus(id, data))
 
 	default:
 		return nil, unimplementedPacketErr(typ)

request-server_test.go

@@ -745,6 +745,23 @@ func TestRequestStatVFS(t *testing.T) {
 	require.Equal(t, expected.Bavail, vfs.Bavail)
 	require.Equal(t, expected.Bfree, vfs.Bfree)
 	require.Equal(t, expected.Blocks, vfs.Blocks)
+
+	checkRequestServerAllocator(t, p)
+}
+
+func TestRequestStatVFSError(t *testing.T) {
+	if runtime.GOOS != "linux" && runtime.GOOS != "darwin" {
+		t.Skip("StatVFS is implemented on linux and darwin")
+	}
+
+	p := clientRequestServerPair(t)
+	defer p.Close()
+
+	_, err := p.cli.StatVFS("a missing path")
+	require.Error(t, err)
+	require.True(t, os.IsNotExist(err))
+
+	checkRequestServerAllocator(t, p)
 }
 
 func TestCleanDisconnect(t *testing.T) {