data_set_manager has test with non-determinstic behavior

[ilan-gold]

• Specific code commit:
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• Environment where the error occurred (Vagrant VM and site conf mode or AWS instance):

Steps to reproduce

Please list all the actions and the input data used:

1. Move the actual test functionality into its own function
2. Run that function inside a while-true loop inside the actual test until it fails

Observed behavior

• The test test_get_with_study_uuid_returns_file_uuid_field fails randomly because the order of nodes serialized/returned is non-deterministic
• This causes the first_node to sometimes be a node lacking a file_uuid field.

Error Traceback (most recent call last): File "/vagrant/refinery/data_set_manager/test_views.py", line 815, in test_get_with_study_uuid_returns_file_uuid_field self.get_with_study_uuid_returns_file_uuid_field() File "/vagrant/refinery/data_set_manager/test_views.py", line 830, in get_with_study_uuid_returns_file_uuid_field raise e AttributeError: 'NoneType' object has no attribute 'uuid'

Expected behavior

• The test should always pass