func TestForceWriteEmpty(t *testing.T) {
type InnerWriteEmpty struct {
    // sth. that isn't zero-len if default, e.g. fixed32:
    ValIn int32 `amino:"write_empty" binary:"fixed32"`
}

type OuterWriteEmpty struct {
    In  InnerWriteEmpty `amino:"write_empty"`
    Val int             `amino:"write_empty" binary:"fixed32"`
}

cdc := amino.NewCodec()

b, err := cdc.MarshalBinaryBare(OuterWriteEmpty{})
assert.NoError(t, err)
assert.Equal(t, []byte{10, 5, 13, 0, 0, 0, 0, 16, 0}, b)

b, err = cdc.MarshalBinaryBare(InnerWriteEmpty{})
assert.NoError(t, err)
assert.Equal(t, []byte{13, 0, 0, 0, 0,}, b)
}