missing UnmarshalJSON method

[nicolasStevenin]

Hi,

When I try to test the repo "tests" it fails with

• go test -compiler gc -ldflags '-X github.com/pquerna/ffjson/version.GitSHA=d49c2bc1aa135aad0c6f4fc2056623ec78f5d5ac -extldflags '''-Wl,-z,relro ''''
  FAIL github.com/pquerna/ffjson/tests [build failed]

github.com/pquerna/ffjson/tests

./ff_invalid_test.go:35:12: cannot use Xstring literal (type *Xstring) as type json.Unmarshaler in argument to testExpectedError:
*Xstring does not implement json.Unmarshaler (missing UnmarshalJSON method)
./ff_invalid_test.go:42:12: cannot use Xstring literal (type *Xstring) as type json.Unmarshaler in argument to testExpectedError:
*Xstring does not implement json.Unmarshaler (missing UnmarshalJSON method)
./ff_invalid_test.go:49:12: cannot use Xstring literal (type *Xstring) as type json.Unmarshaler in argument to testExpectedError:
*Xstring does not implement json.Unmarshaler (missing UnmarshalJSON method)
./ff_invalid_test.go:56:11: cannot use Xarray literal (type *Xarray) as type json.Unmarshaler in argument to testExpectedError:
*Xarray does not implement json.Unmarshaler (missing UnmarshalJSON method)
./ff_invalid_test.go:63:11: cannot use Xarray literal (type *Xarray) as type json.Unmarshaler in argument to testExpectedError:
*Xarray does not implement json.Unmarshaler (missing UnmarshalJSON method)
./ff_invalid_test.go:70:11: cannot use Xarray literal (type *Xarray) as type json.Unmarshaler in argument to testExpectedError:
*Xarray does not implement json.Unmarshaler (missing UnmarshalJSON method)
./ff_invalid_test.go:77:11: cannot use Xarray literal (type *Xarray) as type json.Unmarshaler in argument to testExpectedError:
*Xarray does not implement json.Unmarshaler (missing UnmarshalJSON method)
./ff_invalid_test.go:84:11: cannot use Xarray literal (type *Xarray) as type json.Unmarshaler in argument to testExpectedError:
*Xarray does not implement json.Unmarshaler (missing UnmarshalJSON method)
./ff_invalid_test.go:91:11: cannot use Xint64 literal (type *Xint64) as type json.Unmarshaler in argument to testExpectedError:
*Xint64 does not implement json.Unmarshaler (missing UnmarshalJSON method)
./ff_invalid_test.go:98:12: cannot use Xstring literal (type *Xstring) as type json.Unmarshaler in argument to testExpectedError:
*Xstring does not implement json.Unmarshaler (missing UnmarshalJSON method)
./ff_invalid_test.go:98:12: too many errors

Thank you for your help