@Test
 public void testSamplerHelper2() {
   final double tol = 1e-12;
   final double[] testValues = {
     -1e0, -1e-1, -1e-2, -1e-3, -1e-4, -1e-5, -1e-6, -1e-7, -1e-8, -1e-9, -1e-10, -1e-11, 0.,
     1e-11, 1e-10, 1e-9, 1e-8, 1e-7, 1e-6, 1e-5, 1e-4, 1e-3, 1e-2, 1e-1, 1e0
   };
   for (double testValue : testValues) {
     final double expected = FastMath.expm1(testValue);
     TestUtils.assertRelativelyEquals(
         expected, ZipfRejectionInversionSampler.helper2(testValue) * testValue, tol);
   }
 }
 @Test
 public void testSamplerHelper1Minus1() {
   Assert.assertEquals(Double.POSITIVE_INFINITY, ZipfRejectionInversionSampler.helper1(-1d), 0d);
 }