How true are study.com tests to the curriculum?

[Merlin]

It varies by specific course, and as some have commented the upper-level courses tend to be more focused on testing your ability to apply what you've learned where lower-level courses tend to focus more on understanding concepts.

That said, in general, in taking 20 courses with Study.com, I found that the practice and chapter tests generally draw from the same test bank, which is not the same as the final exam's test bank. But, there is crossover... maybe 25-30% of the questions are the same or very closely worded, some of those may be reversed (as in "what as in which of these is NOT the right answer" types of questions).

For most courses, all the questions are generally taken from the course lectures. So as long as you pay attention to the course material, you should do fine. I found a few exams (databases and systems analysis) that appear to have questions which are drawn from elsewhere (plus they are generally poorly worded) but most courses draw their questions from the course text.