Getting a license to drive in Thailand doesn't involve taking a driving test, as long as you have a valid driving license from your home country.
The validity of that license should be confirmed by your own Embassy.
However, getting the license does involve quite a lot of beurocracy, paper work and a few non driving tests such as eyesight and reflexes.
Having a Thai driving license is fairly useful, and often helps the visitor to avoid fines from police who may see the foreigner in Thailand as "easy pickings".
Theoretically anyone living in Thailand for more than three months should have a Thai drivers license.
The first regulations are that the person should have a Non Immigration B Visa, be in good health and be over eighteen.
The forms are in Thai, so an interpreter is needed to complete the paperwork.
Copies of the passport pages with the applicants details and the visa page have to be signed along with the last entry date page.
Add to this a letter from your home Embassy confirming your residential address, and we can see the paper work is building up.
If you have a work permit, then some of these form are not required - it's best to be prepared though and have as many documents ready, just in case.
Better to have too many signed forms than too few and as anyone who has been in Thailand for any length of time knows, forms with appropriate stamps and signatures go a long way!