adding test for ranking with np.inf

Author: Noah Spies

pandas/tests/test_series.py

@@ -4060,7 +4060,12 @@ def test_rank(self):
         iranks = iseries.rank()
         assert_series_equal(iranks, exp)
 
-
+        values = np.array([-np.inf, -50, -1, -1e-20, -1e-25, -1e-50, 0, 1e-40, 1e-20, 1e-10, 2, 40, np.inf])
+        random_order = np.random.permutation(len(values))
+        iseries = Series(values[random_order])
+        exp = Series(random_order + 1)
+        iranks = iseries.rank()
+        assert_series_equal(iranks, exp)
 
 
     def test_from_csv(self):