Find out what your state requires. To see what homeschool law is all about you can contact the Home School Legal Defense Association. Visit their website at hslda.org.
Define why you feel your homeschool child needs to take a standardized test. If you're concerned of her performance as compared to publicly schooled students, you may want to choose a test that the public school students take in your district.
Choose a test that will make the first testing experience a positive one. If this is the homeschool student's first exposure to standardized tests, choose a test that will build your child's confidence. Consider heavily whether you want to have them tested at their current "grade" level.
Make sure the test mirrors the content you've covered as closely as possible. It is possible to get sample questions and practice tests for most of the standardized written tests available. Check with the test provider for a sample so you can evaluate whether your student has covered that information.
Determine the best testing location. Some standardized tests cannot be performed at home, where the student is used to doing their learning. Some can be given at home, but require a proctor with a degree and a testing certificate. See what the requirements are for your specific test and match the best test to your child's needs.