Divide test in two and extract CONTRIBUTING.md changes into another PR

Author: ca-nguyen

CONTRIBUTING.md

@@ -57,8 +57,8 @@ Before sending us a pull request, please ensure that:
 ### Running the Unit Tests
 
 1. Install tox using `pip install tox`
+1. Install test dependencies, including coverage, using `pip install .[test]`
 1. cd into the aws-step-functions-data-science-sdk-python folder: `cd aws-step-functions-data-science-sdk-python` or `cd /environment/aws-step-functions-data-science-sdk-python`
-1. Install test dependencies, including coverage, using `pip install ".[test]"`
 1. Run the following tox command and verify that all code checks and unit tests pass: `tox tests/unit`
 
 You can also run a single test with the following command: `tox -e py36 -- -s -vv <path_to_file><file_name>::<test_function_name>`  
@@ -80,7 +80,7 @@ You should only worry about manually running any new integration tests that you
 
 1. Create a new git branch:
      ```shell
-     git checkout -b my-fix-branch main
+     git checkout -b my-fix-branch master
      ```
 1. Make your changes, **including unit tests** and, if appropriate, integration tests.
    1. Include unit tests when you contribute new features or make bug fixes, as they help to:

src/stepfunctions/steps/states.py

@@ -221,11 +221,14 @@ def next(self, next_step):
         if self.type in ('Succeed', 'Fail'):
             raise ValueError('Unexpected State instance `{step}`, State type `{state_type}` does not support method `next`.'.format(step=next_step, state_type=self.type))
 
-        # By design, choice states do not have the Next field. Setting default to make it chainable.
+        # By design, Choice states do not have the Next field. Their purpose is to define conditional transitions based
+        # on a set of Choice Rules. They can be viewed as an advanced Next field with multiple possible transitions.
+        # default_choice() sets the default transition to use in the case where none of the Choice Rules are met.
+        # See language spec for more info: https://states-language.net/spec.html#choice-state
         if self.type is 'Choice':
             if self.default is not None:
                 logger.warning(
-                    "Chaining Choice Step: Overwriting %s's current default_choice (%s) with %s",
+                    "Chaining Choice state: Overwriting %s's current default_choice (%s) with %s",
                     self.state_id,
                     self.default.state_id,
                     next_step.state_id

tests/unit/test_steps.py

@@ -368,28 +368,35 @@ def test_chaining_steps():
     assert s2.next_step == s3
 
 
-def test_chaining_choice(caplog):
+def test_chaining_choice():
     s1_pass = Pass('Step - One')
     s2_choice = Choice('Step - Two')
     s3_pass = Pass('Step - Three')
 
-    with caplog.at_level(logging.WARNING):
-        chain1 = Chain([s1_pass, s2_choice, s3_pass])
-        assert caplog.text == ''  # No warning
+    chain1 = Chain([s1_pass, s2_choice, s3_pass])
     assert chain1.steps == [s1_pass, s2_choice, s3_pass]
     assert s1_pass.next_step == s2_choice
     assert s2_choice.default == s3_pass
     assert s2_choice.next_step is None  # Choice steps do not have next_step
     assert s3_pass.next_step is None
 
+
+def test_chaining_choice_with_default(caplog):
+    s1_pass = Pass('Step - One')
+    s2_choice = Choice('Step - Two')
+    s3_pass = Pass('Step - Three')
+
+    s2_choice.default_choice(s3_pass)
+
     # Chain s2_choice when default_choice is already set will trigger Warning
     with caplog.at_level(logging.WARNING):
         Chain([s2_choice, s1_pass])
-        log_message = (
-                "Chaining Choice Step: Overwriting %s's current default_choice (%s) with %s" %
+        expected_warning = (
+                "Chaining Choice state: Overwriting %s's current default_choice (%s) with %s" %
                 (s2_choice.state_id, s3_pass.state_id, s1_pass.state_id)
         )
-        assert log_message in caplog.text
+        assert expected_warning in caplog.text
+        assert 'WARNING' in caplog.text
     assert s2_choice.default == s1_pass
     assert s2_choice.next_step is None  # Choice steps do not have next_step