Use request_cls attribute in contract definition

docs/topics/contracts.rst

@@ -86,8 +86,9 @@ override three methods:
     .. method:: Contract.adjust_request_args(args)
 
         This receives a ``dict`` as an argument containing default arguments
-        for request object. :class:`~scrapy.http.Request` is used
-        if ``request_cls`` is not set on ``args``.
+        for request object. :class:`~scrapy.http.Request` is used by default,
+        but this can be changed with the ``request_cls`` attribute.
+        If multiple contracts in chain have this attribute defined, the last one is used.
 
         Must return the same or a modified version of it.
 

scrapy/contracts/__init__.py

@@ -4,7 +4,6 @@ from functools import wraps
 from inspect import getmembers
 from unittest import TestCase
 
-from scrapy import FormRequest
 from scrapy.http import Request
 from scrapy.utils.spider import iterate_spider_output
 from scrapy.utils.python import get_spec
@@ -50,14 +49,17 @@ class ContractsManager(object):
     def from_method(self, method, results):
         contracts = self.extract_contracts(method)
         if contracts:
-            # prepare request arguments
-            kwargs = {'callback': method}
+            request_cls = Request
+            for contract in contracts:
+                if contract.request_cls is not None:
+                    request_cls = contract.request_cls
+
+            # calculate request args
+            args, kwargs = get_spec(request_cls.__init__)
+            kwargs['callback'] = method
             for contract in contracts:
                 kwargs = contract.adjust_request_args(kwargs)
 
-            request_cls = kwargs.pop('request_cls', Request)
-
-            args, _ = get_spec(request_cls.__init__)
             args.remove('self')
 
             # check if all positional arguments are defined in kwargs
@@ -98,6 +100,7 @@ class ContractsManager(object):
 
 class Contract(object):
     """ Abstract class for contracts """
+    request_cls = None
 
     def __init__(self, method, *args):
         self.testcase_pre = _create_testcase(method, '@%s pre-hook' % self.name)

tests/test_contracts.py

@@ -27,9 +27,9 @@ class ResponseMock(object):
 
 class CustomFormContract(Contract):
     name = 'custom_form'
+    request_cls = FormRequest
 
     def adjust_request_args(self, args):
-        args['request_cls'] = FormRequest
         args['formdata'] = {'name': 'scrapy'}
         return args