The particular IELTS test that you are required to take for the visa depends on the country as well as the sort of immigration visa you are seeking. In most instances, IELTS General Training should be sufficient for all immigration cases; however, there are specific types of immigration visas which require an IELTS Academic test or a certain band for each section. You would do well to verify the testing requirements of your destination country with that country's immigration office prior to booking the test. Resources like FITA Academy can be very useful in helping you familiarize yourself with the format of the test.