Unit tests needed #162
Description
We should add unit tests for existing codebase in order to have a coverage of 80% at least.
Each test class should test the related src class and be located under same package.
E.g. Tile.java src class is under project_16x16.components package (src/project_16x16/components directory). TileTest.java test class must be under project_16x16.components package (test/project_16x16/components directory).
Test class name must have the suffix Test added to the source class under test.
E.g. Tile.java src class to be tested must have a TileTest.java test class.