### Question:
Hexagons { public static double sideLengthToArea(double sideLen) { if (sideLen <= 0.0) { throw new IllegalArgumentException("side length must be > 0"); } return sideLen * sideLen * 1.5 * ROOT3; }  static double sideLengthToArea(double sideLen); static double areaToSideLength(double area); static Hexagon create(double minX, double minY, double sideLen,
            Orientation orientation, CoordinateReferenceSystem crs); static SimpleFeatureSource createGrid(
            ReferencedEnvelope bounds,
            double sideLen,
            Orientation orientation,
            GridFeatureBuilder gridBuilder); static SimpleFeatureSource createGrid(
            ReferencedEnvelope bounds,
            double sideLen,
            double vertexSpacing,
            Orientation orientation,
            GridFeatureBuilder gridFeatureBuilder);  }### Answer:
@Test public void calculateArea() { assertEquals(AREA, Hexagons.sideLengthToArea(SIDE_LEN), TOL); }
@Test(expected=IllegalArgumentException.class) public void calculateAreaInvalidArg() { Hexagons.sideLengthToArea(0.0); }