[lit] Throw in unimplemented method (NFC)

[modocache]

Summary

lit's OneCommandFileTest class implements an abstract method that
raises if called. However, it raises by referencing an undefined
symbol. Instead, raise explicitly by throwing a NotImplementedError.
This is clearer, and appeases Python linters.

[beanz]

LGTM!

[beanz]

Committed in rL283090. Thanks for the patch!

[modocache]

Thanks!

utils/lit/lit/formats/base.py

def getTestsInDirectory(self, testSuite, path_in_suite,
                 test = lit.Test.Test(
                     testSuite, path_in_suite + tuple(suffix.split(os.sep)),
                     localConfig)
                 # FIXME: Hack?
                 test.source_path = path
                 yield test
 
     def createTempInput(self, tmp, test):
-        abstract
+        raise NotImplementedError('This is an abstract method.')
 
     def execute(self, test, litConfig):
         if test.config.unsupported:
             return (lit.Test.UNSUPPORTED, 'Test is unsupported')
 
         cmd = list(self.command)
 
         # If using temp input, create a temporary file and hand it to the