Fix tests for server mode.

moto/datapipeline/responses.py

@@ -10,7 +10,11 @@ class DataPipelineResponse(BaseResponse):
 
     @property
     def parameters(self):
+        # TODO this should really be moved to core/responses.py
+        if self.body:
             return json.loads(self.body.decode("utf-8"))
+        else:
+            return self.querystring
 
     @property
     def datapipeline_backend(self):

tests/test_datapipeline/test_server.py

@@ -16,10 +16,12 @@ def test_list_streams():
     backend = server.create_backend_app("datapipeline")
     test_client = backend.test_client()
 
-    res = test_client.get('/?Action=ListStreams')
+    res = test_client.post('/',
+        data={"pipelineIds": ["ASdf"]},
+        headers={"X-Amz-Target": "DataPipeline.DescribePipelines"},
+    )
 
     json_data = json.loads(res.data.decode("utf-8"))
     json_data.should.equal({
-        "HasMoreStreams": False,
-        "StreamNames": [],
+        'PipelineDescriptionList': []
     })