TextTestResult uses TestCase.__str__() which isn't customisable (vs id() or shortDescription())

[rbtcollins]

BPO	16288
Nosy	@rbtcollins, @merwok, @bitdancer, @voidspace, @cjerdonek

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/voidspace'
closed_at = None
created_at = <Date 2012-10-19.18:34:49.213>
labels = ['easy', 'type-feature']
title = "TextTestResult uses TestCase.__str__() which isn't customisable (vs id() or shortDescription())"
updated_at = <Date 2016-09-13.11:52:14.362>
user = 'https://github.com/rbtcollins'

bugs.python.org fields:

activity = <Date 2016-09-13.11:52:14.362>
actor = 'chris.jerdonek'
assignee = 'michael.foord'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2012-10-19.18:34:49.213>
creator = 'rbcollins'
dependencies = []
files = []
hgrepos = []
issue_num = 16288
keywords = ['easy']
message_count = 15.0
messages = ['173352', '173354', '173355', '173365', '173393', '173394', '173395', '173467', '173468', '173472', '173473', '173474', '173490', '276154', '276256']
nosy_count = 5.0
nosy_names = ['rbcollins', 'eric.araujo', 'r.david.murray', 'michael.foord', 'chris.jerdonek']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue16288'
versions = ['Python 3.4']

Linked PRs

• gh-60492: Allow customizing test names in TextTestResult. #117284

[rbtcollins]

TextTestRunner calls str(TestCase) directly, which makes it hard for testscenarios to rename the test cases as it parameterises them (because __str__ is a descriptor). While testscenarios could use a decorator instead, thats undesirable as the test case object would still need to be customised so that calls to self.id() and self.shortDescription() inside it still return consistent information.

So the relevant code is this:
def getDescription(self, test):
41 if self.descriptions:
42 return test.shortDescription() or str(test)
43 else:
44 return str(test)

What I'd like is to have this be something like:
41 if self.descriptions:
42 return test.shortDescription() or test.id()
43 else:
44 return test.id()

Which would let testscenarios adjust both shortDescriptions and id, and Just Work.

[rbtcollins]

Or anther way this could be done would be to make TestCase.__str__ call self.id(), and then __str__ never needs to be adjusted - id() or shortDescription are the only things to tweak.

[bitdancer]

By "descriptor" I think you really mean it is a special method (ie: looked up on the class only, not on an instance). A descriptor is something else.

This is a feature request and could only be implemented in 3.4. Assuming I'm understanding what you are asking for (which is not certain), as a partial workaround you could reset _testMethodName.

[rbtcollins]

They aren't descriptors? They certainly aren't normal methods:
>>> class foo(object):
...   def __str__(self): return "foo"
... 
>>> f = foo()
>>> f.__str__ = lambda: "bar"
>>> str(f)
'foo'

I *thought* the mechanism by which they can only be replaced by altering the class *was* descriptors, but I gladly seek better info!

_testMethodName is overloaded though: its both 'what is the test method' and 'part of the description or id of the test', so resetting it would be - at best - risky when only changing the description or id.

[bitdancer]

The special handling of special methods is baked into the attribute lookup machinery. The discussion of this is in the language reference somewhere, as is the explanation of what descriptors are and how they work.

[cjerdonek]

So the relevant code is this:
def getDescription(self, test):
...
43 return str(test)
...
What I'd like is to have this be something like:
44 return test.id()

Or anther way this could be done would be to make TestCase.__str__ call self.id()

Note that str(test) and test.id() don't return the same value. The former is the "friendly" name. It is probably intentional that TextTestResult uses the TestCase instance's friendly name in its getDescription() method as opposed to the id.

TextTestRunner calls str(TestCase) directly, which makes it hard for testscenarios to rename the test cases as it parameterises them

What about testscenarios subclassing the TestCase instances as it parametrizes them?

    class ScenariosTestCase(case.__class__):
        def __str__(self):
            return "testscenarios test name..."
    case.__class__ = ScenariosTestCase
    print(str(case))

From the documentation, it looks like testscenarios creates new test objects from the originals anyways. Alternatively (although I don't if testscenarios can control what test runner is being used), TextTestRunner could be subclassed with its own getDescription() method.

[merwok]

http://docs.python.org/reference/datamodel.html#special-method-lookup-for-new-style-classes

[rbtcollins]

testscenarios copies the tests, it doesn't call the constructor for the class; this makes things a lot simpler than trying to reconstruct whatever state the object may have from scratch again.

As for str(test) and test.id() being different - well sure they are today, but I don't know that the str(test) format is /useful/ today, as its not a particularly good str() anyhow. It doesn't identify that its a test instance even.

This suggests two alternatives to me:

• decide that we want three things: id, friendly-id and shortDescription, and have three non-magic methods, which TextTestRunner can call depending on what the user wants to see.
• decide we want two things, id and shortDescription, and TextTestRunner can combine these things to meet the users request. (e.g. id + ' ' + shortDescription)

And separately, as the __str__ isn't particularly good anyhow, perhaps we should take the opportunity to think about what we want from it and adjust it.

[voidspace]

So three including str sounds sufficient to me: short description, long description and repr (with str == repr) for debugging.