it depends on the teacher. I had trained 8 years in one style and then switched. I didn't test for close to a year, then my first test was for sankyu, was awarded nikkyu, tested for ikkyu a year later, then did my shodan test at the same time that others who had started "from scratch" did theirs. As a matter of fact, my teacher had quite long gaps on my subsequent test (4 years to nidan), and now after 20 years of practice, I am getting ready for sandan. I know my teacher didn't want to see any vesitages of my previous training left in my body language; others feel differently. Personally I don't agree with how mine was handled and would have tested sooner, or at least acknowledged all the effort and experience that was there previously. It remains a sore spot.