In my family, we do not separate learning from our daily life. We might spend an hour or more at dinner discussing the pros and cons of a current event or an interesting subject. That might be followed by a PBS special about history or nature. After seeing a great play about the Odyssey, my girls were eager to learn about mythology. We spent weeks finding age-appropriate books, watching educational videos, and playing mythology-themed board games. My daughter's Teen French Cooking Club inspires her to spend hours practicing her newly learned skills (cooking involves reading, measurements, following directions, etc.).
When we found a bird that couldn't fly yesterday, we grabbed a book about birds and discussed how to treat it. After many phone calls we found a wildlife rehabilitator willing to take the bird. Following her instructions, we stabilized the bird, then brought it to her. She was a fascinating person and we spent several hours at her bird sanctuary. We all learned a lot. As a result of that visit, my daughters have volunteered to work with the rehabilitator this summer, helping abandoned baby birds. We went to the library this morning and took out several books on birds and wildlife rehabilitation. This is really a typical day of homeschooling in our household.
Sometimes we spend days or even weeks on an interesting topic. I do not have to force my kids to study or learn -- often, I can barely keep up with them! This teaching method is called "unschooling" and is growing in popularity as parents discover the many advantages of child-led learning.
As for testing, a parent or responsible adult should monitor each child's progress. I do not test my kids; I closely monitor their activities, and can easily assess their comprehension and ability. For parents who wish to have their children tested, standardized tests are available throughout the year depending on the grade and type of test. Nationwide, homeschoolers consistently outperform their schooled peers on every standardized test, and at every grade level.