Test default serializer:

obj.to_string(standard)=0.5

Test default serializer with custom userdata:

obj.to_string(userdata)=0.5

Test explicit serializer with custom userdata:

obj.to_string(custom)=test

Test reset serializer:

obj.to_string(reset)=0.5

obj.to_string(default format)=0.52381

obj.to_string(with global format)=x0.524y

obj.to_string(with thread format)=T0.52X

obj.to_string(long thread format)=Ttttttttttttt0.52xxxxxxxxxxxxxxxxxxX

obj.to_string(back to global format)=x0.524y

obj.to_string(back to default format)=0.52381

obj(12.0).to_string(default format)=12.0

obj(12.0).to_string(%.0f)=12

obj(12.0).to_string(%.0g)=1e+01

obj(12.0).to_string(%.1g)=12.0