TST: Change start date to fit benchmark start date

tests/risk/test_risk_period.py

@@ -385,7 +385,7 @@ class TestRisk(WithTradingEnvironment, ZiplineTestCase):
     def test_partial_month(self):
 
         start_session = self.trading_calendar.minute_to_session_label(
-            pd.Timestamp("1991-01-01", tz='UTC')
+            pd.Timestamp("1993-02-01", tz='UTC')
         )
 
         # 1992 and 1996 were leap years

tests/test_examples.py

@@ -21,9 +21,8 @@ import pandas as pd
 
 from zipline import examples
 from zipline.data.bundles import register, unregister
-from zipline.testing import test_resource_path, copy_market_data
-from zipline.testing.fixtures import WithTmpDir, ZiplineTestCase, \
-    WithTradingEnvironment
+from zipline.testing import test_resource_path
+from zipline.testing.fixtures import WithTmpDir, ZiplineTestCase
 from zipline.testing.predicates import assert_equal
 from zipline.utils.cache import dataframe_cache
 
@@ -54,7 +53,6 @@ class ExamplesTests(WithTmpDir, ZiplineTestCase):
             serialization='pickle',
         )
 
-
     @parameterized.expand(sorted(examples.EXAMPLE_MODULES))
     def test_example(self, example_name):
         actual_perf = examples.run_example(