Test, test, test....

[yhoriuchi]

We should follow all the instructions and test whether the software works properly. We need to do the following:

1. Use our 8 replication data and estimate choice-level and profile-level MMs and AMCEs.
2. Try three different ways to estimate SEs.
3. Try to remove or not remove ties
4. Try clustered and not-clustered standard errors
5. Importantly, we should try "wrong" arguments -- There should be numerous ways to set arguments incorrectly. Please consider these wrong settings as much as possible. It is also important to check whether an easy-to-understand and "correct" error message is presented to each "wrong" setting.
6. Try various options for plot().

[yhoriuchi]

In addition to testing the package using as many data sets as possible (for as many settings, including "wrong" arguments, as possible), it may be worth testing the package using the following package. https://testthat.r-lib.org/index.html. @katieclayton and @Mayya-Komisarchik , can you look into it?