MAINT: Refactored unit tests to remove duplication

of arguments to factory.create methods.

Also added checking of the perf period cost basis results after each txn.

tests/test_perf_tracking.py

@@ -13,6 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import division
+
 import collections
 import logging
 import operator
@@ -23,7 +25,7 @@ import datetime
 import pytz
 import itertools
 
-from six.moves import range
+from six.moves import range, zip
 
 import zipline.utils.factory as factory
 import zipline.finance.performance as perf
@@ -925,26 +927,23 @@ shares in position"
         )
 
     def test_cost_basis_calc(self):
-        trades = factory.create_trade_history(
-            1,
-            [10, 11, 11, 12],
-            [100, 100, 100, 100],
-            onesec,
-            self.sim_params
-        )
-
-        transactions = factory.create_txn_history(
+        history_args = (
             1,
             [10, 11, 11, 12],
             [100, 100, 100, 100],
             onesec,
             self.sim_params
         )
+        trades = factory.create_trade_history(*history_args)
+        transactions = factory.create_txn_history(*history_args)
 
         pp = perf.PerformancePeriod(1000.0)
 
-        for txn in transactions:
+        average_cost = 0
+        for i, txn in enumerate(transactions):
             pp.execute_transaction(txn)
+            average_cost = (average_cost * i + txn.price) / (i + 1)
+            self.assertEqual(pp.positions[1].cost_basis, average_cost)
 
         for trade in trades:
             pp.update_last_sale(trade)
@@ -975,14 +974,14 @@ shares in position"
             100,
             trades[-1].dt + onesec)
 
-        saleTxn = create_txn(
+        sale_txn = create_txn(
             down_tick,
             10.0,
             -100)
 
         pp.rollover()
 
-        pp.execute_transaction(saleTxn)
+        pp.execute_transaction(sale_txn)
         pp.update_last_sale(down_tick)
 
         pp.calculate_performance()
@@ -1003,9 +1002,13 @@ shares in position"
 
         pp3 = perf.PerformancePeriod(1000.0)
 
-        transactions.append(saleTxn)
-        for txn in transactions:
+        average_cost = 0
+        for i, txn in enumerate(transactions):
             pp3.execute_transaction(txn)
+            average_cost = (average_cost * i + txn.price) / (i + 1)
+            self.assertEqual(pp3.positions[1].cost_basis, average_cost)
+
+        pp3.execute_transaction(sale_txn)
 
         trades.append(down_tick)
         for trade in trades: