To develop test suite(s) for border adjustment calculator

[GoFroggyRun]

There is currently no test suite for border adjustment calculator, and thus, when making changes to its source code, we might potentially introduce some errors or bugs.

To make us feel more comfortable when making any changes, I'd like to add three types of test suites:

1. Basic test that verifies Shiny app's connectivity

2. Control test that ensures all widgets are working properly

3. Output test that validates real-time calculations against static corner cases

[GoFroggyRun]

After PR #8 being merged, item 3 listed above is, functional wise, completed. The next step to improve efficiency shall be be working on automated script sync so that core scripts (that involves calculations) in test-numeric.R and ui.R are updated simultaneously.

On the other hand, the script for basic test is finished. There are, however, some unexpected errors from Rselenium package that I wasn't able to deal with for the moment. I'll work on this test, and widget tests, after finishing up all numeric tests, which I think is of more importance.