Added the project to Eclipse and set up JUnit.

Added JUnit to classpath
Created 9 unit tests for getValue().

The tests cover positive/negative/zero values with different units.
Created 9 unit tests for getUnits().

The three units combined with random positive, negative, and zero
values.
Created 27 unit tests for changeUnits.

Redefined the error margin to be less demanding.
Simplified the getValue() tests by creating a method executeGetValue which is the common procedure of all the tests.

Doing this will allow the tests to be more readable.
Simplified the getUnits() tests by creating a method executeGetUnits.

This way, the code is more readable and less clustered.