'Fail if C{instance} is not an instance of the given class or of
one of the given classes.
@param instance: the object to test the type (first argument of the
C{isinstance} call).
@type instance: any.
@param classOrTuple: the class or classes to test against (second
argument of the C{isinstance} call).
@type classOrTuple: class, type, or tuple.
@param message: Custom text to include in the exception text if the
assertion fails.'

def assertIsInstance(self, instance, classOrTuple, message=None):

    if (not isinstance(instance, classOrTuple)):
        if (message is None):
            suffix = ''
        else:
            suffix = (':    ' + message)
        self.fail(('%r    is    not    an    instance    of    %s%s' % (instance, classOrTuple, suffix)))
