|MadSci Network: Chemistry|
A full answer to your question would constitute essentially doing your science fair project for you, which would be unfair to other participants. Clearly, you've not yet fully explored the subject - a simple Web search for 'enteric coating' would produce e.g. http://en.wikipedia.org/wiki/Enteric_coating as well as educate you on the subject of major differences in gastric vs enteric enviromnent.
Similarly, http://en.wikipedia.org/wiki/Digestion provides a lot of other information that you may need (e.g. that stomach pH should be acidic, and how acidic, and that intestinal pH should be mildly basic).
You can't fully simulate gastric and enteric environment without using fairly complex mixtures of chemicals, enzymes, etc. Also, the effectiveness of any given pill depends on much more complex parameters than just how quickly it dissolves or where.
As a start towards simulating pill dissolution in enteric fluid you have to first expose the pill to acidic environment (with appropriate enzymes in the mix) followed by neutralization with carbonate (normally produced by pancreas) and treatment with basic liquid containing enzymes such as trypsin, chymotrypsin, etc. You also need a reliable method to monitor completeness of dissolution (i.e. beyond observing it with your eyes) as well as adequate number of repetitions and controls, for accuracy and reproducibility.
Try the links in the MadSci Library for more information on Chemistry.