### Question:
Tileable implements Entity { public boolean onGrid() { return tile != null; }  abstract boolean allowsConnection(Direction direction); abstract boolean accepts(Direction direction, Marble marble); abstract void accept(Direction direction, Marble marble); boolean isConnected(Direction direction); boolean isReleasable(Direction direction, Marble marble); void release(Direction direction, Marble marble); Tile getTile(); void setTile(Tile tile); Set<TileableListener> getListeners(); boolean addListener(TileableListener listener); boolean removeListener(TileableListener listener); boolean onGrid();  }### Answer:
@Test public void onGrid() { Tileable tileable = grid.get(0, 0).getTileable(); assertThat(tileable.onGrid()).isTrue(); }
@Test public void notOnGrid() { Tileable tileable = new HorizontalTrack(); assertThat(tileable.onGrid()).isFalse(); }