Read the College Board site for infomation about AP tests. Do not just take my word for what the AP test is like.
Main page College Board page for AP Tests
List of the different AP tests, click which you are curious about to view.
Here is one, the US History course description page.
In my opinion, this is a huge span of information. A friend said to me, "The teachers know what is on the test." When you see the list of the content of the class, saying that the bulk of the test is on 200 of the nation's 350 year history is still painting the canvas with a wide brush. I disagree with her, because it is certainly not the same as when Mrs. Smith writes her own essay questions.
If you are curious what the essay or what they call the "free response" questions are like, you can read the questions from past years for US History on the site at this link.
I am impressed by what seems to be academic rigor. What bothers me is the fact that to do this work honestly is a huge task. Admitted cheating by schooled kids such as revealed in the documentary movie Race to Nowhere is disturbing. That may account for student's higher grades in the class compared to the test score (assuming they were not able to cheat on the test itself).
I do not like the notion that if a high schooled student does not do AP work that they are not doing enough. It seems to me that the more students enroll into college the more competition there is for spots so they keep raising the bar for admissions. The statement that there are over 37,000 high schools now and that even the valedictorians of those schools won't all get into top colleges because there are just not enough slots is scary.
I will close by saying that the College Board has been redesigning the AP tests to try to add more critical thinking and thinking skills instead of just memorization and partoting of facts. Critics had said that our country and world does not need good memorizers, it needs people who can actually think. The changes are rolling out over multiple years. This has been discussed in the media. If you're curious do some internet searching for more information.