Fix error in Categorical prior and add tests

bilby/core/prior/analytical.py

@@ -1469,7 +1469,7 @@ class Categorical(Prior):
         =======
         Union[float, array_like]: Rescaled probability
         """
-        return np.round(val * self.maximum)
+        return np.floor(val * (1 + self.maximum))
 
     def prob(self, val):
         """Return the prior probability of val.

test/core/prior/analytical_test.py

@@ -15,13 +15,19 @@ class TestCategoricalPrior(unittest.TestCase):
         self.assertTrue(in_prior)
 
     def test_array_sample(self):
-        categorical_prior = bilby.core.prior.Categorical(3)
-        N = 1000
+        ncat = 4
+        categorical_prior = bilby.core.prior.Categorical(ncat)
+        N = 100000
         s = categorical_prior.sample(N)
         zeros = np.sum(s == 0)
         ones = np.sum(s == 1)
         twos = np.sum(s == 2)
-        self.assertEqual(zeros + ones + twos, N)
+        threes = np.sum(s == 3)
+        self.assertEqual(zeros + ones + twos + threes, N)
+        self.assertAlmostEqual(zeros / N, 1 / ncat, places=int(np.log10(np.sqrt(N))))
+        self.assertAlmostEqual(ones / N, 1 / ncat, places=int(np.log10(np.sqrt(N))))
+        self.assertAlmostEqual(twos / N, 1 / ncat, places=int(np.log10(np.sqrt(N))))
+        self.assertAlmostEqual(threes / N, 1 / ncat, places=int(np.log10(np.sqrt(N))))
 
     def test_single_probability(self):
         N = 3