Small changes to docs and tests for percentchange

Author: palewire

census_data_aggregator/__init__.py

@@ -370,14 +370,16 @@ def approximate_percentchange(pair_old, pair_new):
                 (61393366, 202289)
 
     Examples:
+        The change of percentage of single women in suburban Virginia,
+        taken from the bureau's official example as well as data `gathered elsewhere`_.
 
         >>> approximate_percentchange((135173, 3860), (139301, 4047))
         (3.0538643072211165, 4.198069852261231)
 
-        2017 value from: https://www.fairfaxcounty.gov/demographics/sites/demographics/files/assets/acs/acs2017.pdf
-
     ... _official guidelines:
         https://www.documentcloud.org/documents/6177941-Acs-General-Handbook-2018-ch08.html#document/p8
+    ... _gathered elsewhere:
+        https://www.fairfaxcounty.gov/demographics/sites/demographics/files/assets/acs/acs2017.pdf
     """
     # Pull out the values
     estimate_old, moe_old = pair_old

test.py

@@ -3,7 +3,10 @@
 import doctest
 import unittest
 import census_data_aggregator
-from census_data_aggregator.exceptions import DesignFactorWarning, DataError
+from census_data_aggregator.exceptions import (
+    DesignFactorWarning,
+    DataError
+)
 
 
 class CensusErrorAnalyzerTest(unittest.TestCase):
@@ -85,6 +88,14 @@ def test_median(self):
         ]
         census_data_aggregator.approximate_median(top_median, design_factor=1.5)
 
+    def test_percentchange(self):
+        estimate, moe = census_data_aggregator.approximate_percentchange(
+            (135173, 3860),
+            (139301, 4047)
+        )
+        self.assertAlmostEqual(estimate, 3.0538643072211165)
+        self.assertAlmostEqual(moe, 4.198069852261231)
+
     def test_exception(self):
         DesignFactorWarning().__str__()