TST: Adds test for symbol changes

tests/test_assets.py

@@ -18,6 +18,7 @@ Tests for the zipline.assets package
 """
 from contextlib import contextmanager
 from datetime import datetime, timedelta
+from functools import partial
 import pickle
 import sys
 from types import GetSetDescriptorType
@@ -25,7 +26,6 @@ from unittest import TestCase
 import uuid
 import warnings
 
-from nose.tools import raises
 from nose_parameterized import parameterized
 from numpy import full, int32, int64
 import pandas as pd
@@ -483,6 +483,97 @@ class AssetFinderTestCase(WithTradingCalendar, ZiplineTestCase):
         self.assertEqual(2, finder.lookup_symbol('BRK_A', None, fuzzy=True))
         self.assertEqual(2, finder.lookup_symbol('BRK_A', dt, fuzzy=True))
 
+    def test_lookup_symbol_change_ticker(self):
+        T = partial(pd.Timestamp, tz='utc')
+        metadata = pd.DataFrame.from_records(
+            [
+                # sid 0
+                {
+                    'symbol': 'A',
+                    'start_date': T('2014-01-01'),
+                    'end_date': T('2014-01-05'),
+                },
+                {
+                    'symbol': 'B',
+                    'start_date': T('2014-01-06'),
+                    'end_date': T('2014-01-10'),
+                },
+
+                # sid 1
+                {
+                    'symbol': 'C',
+                    'start_date': T('2014-01-01'),
+                    'end_date': T('2014-01-05'),
+                },
+                {
+                    'symbol': 'A',  # claiming the unused symbol 'A'
+                    'start_date': T('2014-01-06'),
+                    'end_date': T('2014-01-10'),
+                },
+            ],
+            index=[0, 0, 1, 1],
+        )
+        self.write_assets(equities=metadata)
+        finder = self.asset_finder
+
+        # note: these assertions walk forward in time, starting at assertions
+        # about ownership before the start_date and ending with assertions
+        # after the end_date; new assertions should be inserted in the correct
+        # locations
+
+        # no one held 'A' before 01
+        with self.assertRaises(SymbolNotFound):
+            finder.lookup_symbol('A', T('2013-12-31'))
+
+        # no one held 'C' before 01
+        with self.assertRaises(SymbolNotFound):
+            finder.lookup_symbol('C', T('2013-12-31'))
+
+        for asof in pd.date_range('2014-01-01', '2014-01-05', tz='utc'):
+            # from 01 through 05 sid 0 held 'A'
+            assert_equal(
+                finder.lookup_symbol('A', asof),
+                finder.retrieve_asset(0),
+                msg=str(asof),
+            )
+
+            # from 01 through 05 sid 1 held 'C'
+            assert_equal(
+                finder.lookup_symbol('C', asof),
+                finder.retrieve_asset(1),
+                msg=str(asof),
+            )
+
+        # no one held 'B' before 06
+        with self.assertRaises(SymbolNotFound):
+            finder.lookup_symbol('B', T('2014-01-05'))
+
+        # no one held 'C' after 06, however, no one has claimed it yet
+        # so it still maps to sid 1
+        assert_equal(
+            finder.lookup_symbol('C', T('2014-01-07')),
+            finder.retrieve_asset(1),
+        )
+
+        for asof in pd.date_range('2014-01-06', '2014-01-11', tz='utc'):
+            # from 06 through 10 sid 0 held 'B'
+            # we test through the 11th because sid 1 is the last to hold 'B'
+            # so it should ffill
+            assert_equal(
+                finder.lookup_symbol('B', asof),
+                finder.retrieve_asset(0),
+                msg=str(asof),
+            )
+
+            # from 06 through 10 sid 1 held 'A'
+            # we test through the 11th because sid 1 is the last to hold 'A'
+            # so it should ffill
+            assert_equal(
+                finder.lookup_symbol('A', asof),
+                finder.retrieve_asset(1),
+                msg=str(asof),
+            )
+
     def test_lookup_symbol(self):
 
         # Incrementing by two so that start and end dates for each
@@ -551,7 +642,7 @@ class AssetFinderTestCase(WithTradingCalendar, ZiplineTestCase):
 
         self.assertEqual(
             str(e.exception),
-            "Ambigious ownership of 'MULTIPLE', multiple companies held this"
+            "Ambiguous ownership of 'MULTIPLE', multiple companies held this"
             " ticker over the following ranges:\n"
             "[('2010-01-01 00:00:00', '2012-01-01 00:00:00'),"
             " ('2011-01-01 00:00:00', '2012-01-01 00:00:00')]",