Fix pulp cbc cmd solver params

[marcusreaiche]

PR

• The PULP_CBC_CMD solver is not correctly processing some parameters when calling CBC.
• This is the case for the presolve and cuts arguments.
• For example, when calling solve with presolve=False, the option presolve on is still passed to the command line.
• Moreover, Pulp's documentation on PULP_CBC_CMD states that the strong parameter is of type bool.
• However, it is of type int as mentioned is CBC's help.
• New unit tests that check the command line instruction passed to CBC are created.

The following Google Colab Notebook presents all the issues and the corresponding fixes.

https://colab.research.google.com/drive/18afePVGohf9Bumns6ziiXjuoAI6SrJZL?usp=sharing

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[marcusreaiche]

Commit 29ab059 removed the type annotations for compatibility with older Python versions.

[pchtsp]

Thanks, until now, we had them as flags of None/ not None. I guess it makes sense to be able to pass False if we want to deactivate them.

Since these tests only affect CBC, I recommend to add them as methods of the CBC class:

pulp/pulp/tests/test_pulp.py

Lines 1439 to 1443 in 6af3801

	class PULP_CBC_CMDTest(BaseSolverTest.PuLPTest):
	solveInst = PULP_CBC_CMD

[marcusreaiche]

Hey Franco,

Thanks for your recommendations.

• I moved the new tests to the PULP_CBC_CMDTest class.
• I also moved the helper methods implemented in pulp/tests/utilities.py to the same class as static methods
  • Since they are only used to extract information from the CBC log file, I believe it is more logical to include them within this class.

Please let me know if you have any other suggestions.