TurboTax follows the way that the IRS handles HSAs. Contributions are considered taxable by the IRS until you have completed the 8889 to show that you had sufficient HDHP coverage.
HOWEVER, you don't complete form 8889 yourself; TurboTax does that for you as you go through the HSA interview (Search for hsa (lower case) and jump to it). If you are doing the total step by step interview, TurboTax will bring you here (eventually). In any case, you will be unable to e-file the return without the 8889 because the return will fail in the federal review. There is no way for the taxpayer to file a return without the 8889, unless he/she ignores the error messages in the review.
Note that once you enter the HSA interview, you need to go all the way to the end, as there are questions all the way through the interview that affect your deduction.
