### Question:
Hexagons { public static double areaToSideLength(double area) { if (area <= 0.0) { throw new IllegalArgumentException("area must be > 0"); } return Math.sqrt(area * 2.0 / 3.0 / 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 calculateSideLen() { assertEquals(SIDE_LEN, Hexagons.areaToSideLength(AREA), TOL); }
@Test(expected=IllegalArgumentException.class) public void calculateSideLenInvalidArg() { Hexagons.areaToSideLength(0.0); }