add pyyaml to test_require

[LuiggiTenorioK]

PR to fix our CI pipeline because pyyaml is not installed indirectly anymore by one of our dependencies and is used inside test_rocrate.py.

I tried to change it to ruamel.yaml by doing:

diff --git a/test/unit/provenance/test_rocrate.py b/test/unit/provenance/test_rocrate.py
index 8e0b4e1c..134c4190 100644
--- a/test/unit/provenance/test_rocrate.py
+++ b/test/unit/provenance/test_rocrate.py
@@ -6,7 +6,8 @@ from subprocess import CalledProcessError
 from tempfile import TemporaryDirectory
 from unittest import TestCase
 
-import yaml
+from io import StringIO
+from ruamel.yaml import YAML
 from mock import Mock, patch
 from rocrate.rocrate import File
 from rocrate.rocrate import ROCrate
@@ -48,7 +49,10 @@ class TestRoCrate(TestCase):
         Path(conf_dir, 'metadata').mkdir()
         unified_config = Path(conf_dir, 'metadata/experiment_data.yml')
         unified_config.touch()
-        unified_config.write_text(yaml.dump(as_conf.experiment_data))
+        stream = StringIO()
+        YAML().dump(as_conf.experiment_data, stream)
+        yaml_string = stream.getvalue()
+        unified_config.write_text(yaml_string)
         as_conf.current_loaded_files = {unified_config: 0}
 
     def test_add_dir_and_files_empty_folder(self):

but ruaml.yaml prevents you to write a in the file with an arbitrary object type which is necessary for the TestRoCrate::test_rocrate_invalid_parameter_type test. Alternatively, I added pyyaml to the test_require as the easiest solution.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.92%. Comparing base (3706cb9) to head (2ca9935).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2047   +/-   ##
=======================================
  Coverage   48.92%   48.92%           
=======================================
  Files          72       72           
  Lines       17543    17543           
  Branches     3415     3415           
=======================================
  Hits         8583     8583           
  Misses       8156     8156           
  Partials      804      804           

Flag	Coverage Δ
fast-tests	48.92% <ø> (ø)

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