test_nonhash_value tests the lookup of an Enum Member from a value.

The current test does not exercise the iteration over values completely -- the if-clause being redundant wrt the existing test.

My patch adds an additional test which requires the if-clause.

I'm not sure what you are talking about.  Here's the code:

    try:
        if value in cls._value2member_map_:
            return cls._value2member_map_[value]
    except TypeError:
        # not there, now do long search -- O(n) behavior
        for member in cls._member_map_.values():
            if member.value == value:
                return member

Here's the test:

    self.assertEqual(ColorInAList([1]), ColorInAList.red)

In order for that test to work, the first if (in the try) raises a TypeError, then execution falls into the except block and each member is tested for equality until one matches (via the if) -- so what is your added test doing that isn't already being done?

Sorry -- I could have been clearer :

The conditional:

 if member.value == value:

Is redundant as the tests stand.  If you comment it out -- everything works. So therefore we are missing a test.

The current test works, as red is the first value to pop out of the value() list.  

This makes the if-clause fragile for future maintenance.  So we need another test to ensure the loop is covered.

It's a coverage issue -- where although the code is executed by the test, and the code is correct, the test is not complete enough for the code.

CliffM added the comment:
>
> Sorry -- I could have been clearer :
>
> The conditional:
>
>   if member.value == value:
>
> Is redundant as the tests stand.  If you comment it out -- everything works. So therefore we are missing a test.

Are you saying that you are commenting out the if test, but leaving in the return member?

> This makes the if-clause fragile for future maintenance.  So we need another test to ensure the loop is covered.

In case Python for loops suddenly stop working?

Sorry to be so dense, but I am not understanding the point you are trying to make... ahhhhhh!  Are trying to guard 
against the possibility that in the future someone might accidentally delete the if test, and the unit test won't catch 
it?  That certainly is a good reason to test values further into the loop.

Yes it's purely a coverage issue.  I must try to be more explicit (rather than implicit).

Well, I would say it's half a coverage issue, half a guard against accidental deletion of the if test.  :)

New changeset 89f6abc2e115 by Ethan Furman in branch 'default':
Close #19252: better test coverage for Enum.  Thanks, CliffM
http://hg.python.org/cpython/rev/89f6abc2e115