11i: Tax button not calculating taxes on invoice

While I usually focus on R12, I believe that it is important to not forget that people are still on 11i, so when I ran across article "11i: Invoice Tax Not Being Computed Via Calculate Tax Button" on My Oracle Support from note ID 2014831.1 I wanted to understand how big of an issue this is.  Now only is there an issue, but this details several different test scenarios that you can add to your testing suites to make sure you do not encounter this type of issue in the future!