TST: new test for str to small float conversion dtype (#29372)
TST: new test for str to small float conversion dtype (#29372)

* add str to small float conversion type test

* restrucutre test

dsm054/pandas,datapythonista/pandas,jorisvandenbossche/pandas,dsm054/pandas,dsm054/pandas,dsm054/pandas,jorisvandenbossche/pandas,datapythonista/pandas,jreback/pandas,rs2/pandas,gfyoung/pandas,jorisvandenbossche/pandas,TomAugspurger/pandas,pandas-dev/pandas,pandas-dev/pandas,rs2/pandas,jreback/pandas,gfyoung/pandas,pandas-dev/pandas,jreback/pandas,gfyoung/pandas,pandas-dev/pandas,dsm054/pandas,rs2/pandas,gfyoung/pandas,gfyoung/pandas,TomAugspurger/pandas,jorisvandenbossche/pandas,jreback/pandas,datapythonista/pandas,datapythonista/pandas,TomAugspurger/pandas,TomAugspurger/pandas,rs2/pandas,jreback/pandas