TST: overwrite_sim_params=False in tests when using list of sources

When specifying a list of sources to algorithm.py:run in a unit test,
specify overwrite_sim_params=False to suppress the unnessary
UserWarning.

tests/test_algorithm.py

@@ -331,7 +331,7 @@ class TestTransformAlgorithm(TestCase):
             sim_params=sim_params,
             sids=[0, 1, 133]
         )
-        algo.run([self.source, self.df_source])
+        algo.run([self.source, self.df_source], overwrite_sim_params=False)
         self.assertEqual(len(algo.sources), 2)
 
     def test_df_as_input(self):

tests/test_algorithm_gen.py

@@ -226,5 +226,5 @@ class AlgorithmGeneratorTestCase(TestCase):
         sim_params = create_simulation_parameters(num_days=1,
                                                   data_frequency='minute')
         algo = TestAlgo(self, sim_params=sim_params)
-        algo.run(source=[])
+        algo.run(source=[], overwrite_sim_params=False)
         self.assertEqual(algo.datetime, sim_params.last_close)

tests/test_tradesimulation.py

@@ -57,7 +57,7 @@ class TestTradeSimulation(TestCase):
             emission_rate=emission_rate)
 
         algo = BeforeTradingAlgorithm(sim_params=params)
-        algo.run(source=[])
+        algo.run(source=[], overwrite_sim_params=False)
 
         self.assertEqual(algo.perf_tracker.day_count, num_days)
         self.assertTrue(params.trading_days.equals(