nose/case.{Function,Method}TestCase: have consistent __repr__

Tests were added in the previous commit which showed that modifying a
mutable object given as an argument to a test case during the execution of
the test case results in the __repr__ of the test case also changing (if
the __repr__ of the object also changed). This was caused by creating a
__repr__ of the test args on the fly, and because the summary line is
printed *before* the test is executed and failure details are printed
*after* the test is executed, this can result in the two lines having
different __repr__s of the passed in arguments (see the previous commit
message for an example of the output).

This commit fixes the issue by storing a __repr__ of the argument tuple
when the *TestCase is instantiated and using that to create all __repr__s
of the *TestCase. Note that the `if` for when no args are given had to be
changed because `repr(tuple())` is '()', which is truthy.

nose/case.py

@@ -239,6 +239,7 @@ def __init__(self, test, setUp=None, tearDown=None, arg=tuple(),
         self.setUpFunc = setUp
         self.tearDownFunc = tearDown
         self.arg = arg
+        self.arg_repr = repr(self.arg)
         self.descriptor = descriptor
         TestBase.__init__(self)
 
@@ -282,7 +283,7 @@ def __str__(self):
         else:
             name = func.__name__
         name = "%s.%s" % (func.__module__, name)
-        if arg:
+        if not arg == '()':
             name = "%s%s" % (name, arg)
         # FIXME need to include the full dir path to disambiguate
         # in cases where test module of the same name was seen in
@@ -299,9 +300,9 @@ def _descriptors(self):
         are returned.
         """
         if self.descriptor:
-            return self.descriptor, self.arg
+            return self.descriptor, self.arg_repr
         else:
-            return self.test, self.arg
+            return self.test, self.arg_repr
 
 
 class MethodTestCase(TestBase):
@@ -338,6 +339,7 @@ def __init__(self, method, test=None, arg=tuple(), descriptor=None):
         self.method = method
         self.test = test
         self.arg = arg
+        self.arg_repr = repr(self.arg)
         self.descriptor = descriptor
         if isfunction(method):
             raise ValueError("Unbound methods must be wrapped using pyversion.unbound_method before passing to MethodTestCase")
@@ -357,7 +359,7 @@ def __str__(self):
         name = "%s.%s.%s" % (self.cls.__module__,
                              self.cls.__name__,
                              name)
-        if arg:
+        if not arg == '()':
             name = "%s%s" % (name, arg)
         return name
     __repr__ = __str__
@@ -392,6 +394,6 @@ def _descriptors(self):
         or function are returned.
         """
         if self.descriptor:
-            return self.descriptor, self.arg
+            return self.descriptor, self.arg_repr
         else:
-            return self.method, self.arg
+            return self.method, self.arg_repr