TravelTimeCalculator: Further Improvements to the Database (TDD)

Test: Check if dbHelper can add information to an existing entry (continued)

Currently, it is only possible to add information to the database if there is no entry at all for the coordinates.

If I add a direction for the mode "WALKING" to an empty SQLite database using INSERT, it will look like this:

There is data only for the mode "WALKING" in this entry. The other ones are "null".

If I'd like to fill in information about the mode "DRIVING" using INSERT for the same coordinate, the constraint that I used to define the database will prevent me from doing that.

Instead, I need to use the SQLite "UPDATE" command when there is already entries for that direction. 

Using the method checkIfCoordinateExist, to decide whether to insert or update entries, with or without reversed coordinates, I was able to add directions in reversed diretions.

With those changes, I was able to pass the new TDD test case.

Test: Get Duration and Distance for All Modes for Coordinates

I made similar changes in the code to be able to get reversed directions for all modes.

Finally, I added a method for printing the contents of the database to the console.

Next step

Soon, I'll be able to continue working with the app itself, instead of focusing on the database. 

First, I need to define which coordinates the app should scan for, given the center and zoom of the current map view.