diff --git a/force_bdss/cli/tests/test_execution.py b/force_bdss/cli/tests/test_execution.py
index 3202beee1ddbe86d1e31833a86a09ae16770b554..c6cdd6a34b6368af3275c0b110e428ca1ccf7e1e 100644
--- a/force_bdss/cli/tests/test_execution.py
+++ b/force_bdss/cli/tests/test_execution.py
@@ -26,7 +26,7 @@ class TestExecution(unittest.TestCase):
     def test_plain_invocation_mco(self):
         with cd(fixtures.dirpath()):
             try:
-                subprocess.check_output(["force_bdss", "test_empty.json"],
+                subprocess.check_output(["force_bdss", '--help'],
                                         stderr=subprocess.STDOUT)
             except subprocess.CalledProcessError:
                 self.fail("force_bdss returned error at plain invocation.")
diff --git a/force_bdss/core_mco_driver.py b/force_bdss/core_mco_driver.py
index c0ff9fa016664685d4607612a4425129f764b084..733b34b8a07c06a662c72b8f7c25bf0b7729071f 100644
--- a/force_bdss/core_mco_driver.py
+++ b/force_bdss/core_mco_driver.py
@@ -3,6 +3,7 @@ import logging
 
 from traits.api import on_trait_change, Instance, List
 
+from force_bdss.core.verifier import verify_workflow
 from force_bdss.ids import InternalPluginID
 from force_bdss.mco.base_mco import BaseMCO
 from force_bdss.notification_listeners.base_notification_listener import \
@@ -25,6 +26,21 @@ class CoreMCODriver(BaseCoreDriver):
 
     @on_trait_change("application:started")
     def application_started(self):
+        try:
+            workflow = self.workflow
+        except Exception:
+            log.exception("Unable to open workflow file.")
+            sys.exit(1)
+
+        errors = verify_workflow(workflow)
+
+        if len(errors) != 0:
+            log.error("Unable to execute workflow due to verification "
+                      "errors :")
+            for err in errors:
+                log.error(err.error)
+            sys.exit(1)
+
         try:
             mco = self.mco
         except Exception:
@@ -51,13 +67,8 @@ class CoreMCODriver(BaseCoreDriver):
         self.listeners[:] = []
 
     def _mco_default(self):
-        try:
-            workflow = self.workflow
-        except Exception:
-            log.exception("Unable to open workflow file.")
-            raise
 
-        mco_model = workflow.mco
+        mco_model = self.workflow.mco
         if mco_model is None:
             log.info("No MCO defined. Nothing to do. Exiting.")
             sys.exit(0)
diff --git a/force_bdss/tests/fixtures/test_dummy.json b/force_bdss/tests/fixtures/test_dummy.json
new file mode 100644
index 0000000000000000000000000000000000000000..36ec5c0587db0f2d7d2bd06170c0b98f598a3a83
--- /dev/null
+++ b/force_bdss/tests/fixtures/test_dummy.json
@@ -0,0 +1,45 @@
+{
+    "version": "1",
+    "workflow": {
+        "mco": {
+            "id": "force.bdss.enthought.plugin.test.v0.factory.dummy_mco",
+            "model_data": {
+                "parameters": [
+                    {
+                        "id": "force.bdss.enthought.plugin.test.v0.factory.dummy_mco.parameter.dummy_mco_parameter",
+                        "model_data": {
+                            "name": "foo",
+                            "type": "PRESSURE"
+                        }
+                    }
+                ]
+            }
+        },
+        "execution_layers": [
+            [
+                {
+                    "id": "force.bdss.enthought.plugin.test.v0.factory.dummy_data_source",
+                    "model_data": {
+                        "power": 1.0,
+                        "cuba_type_in": "PRESSURE",
+                        "cuba_type_out": "PRESSURE",
+                        "input_slot_info": [
+                            {
+                                "source": "Environment",
+                                "name": "foo"
+                            }
+                        ],
+                        "output_slot_info": [
+                            {
+                                "name": "bar",
+                                "is_kpi": true
+                            }
+                        ]
+                    }
+                }
+            ]
+        ],
+        "notification_listeners": [
+        ]
+    }
+}
diff --git a/force_bdss/tests/fixtures/test_probe.json b/force_bdss/tests/fixtures/test_probe.json
new file mode 100644
index 0000000000000000000000000000000000000000..2eba16d229b756c737c537fc36cd3cd61bd3e528
--- /dev/null
+++ b/force_bdss/tests/fixtures/test_probe.json
@@ -0,0 +1,47 @@
+{
+    "version": "1",
+    "workflow": {
+        "mco": {
+            "id": "force.bdss.enthought.plugin.test.v0.factory.probe_mco",
+            "model_data": {
+                "parameters": [
+                    {
+                        "id": "force.bdss.enthought.plugin.test.v0.factory.probe_mco.parameter.probe_mco_parameter",
+                        "model_data": {
+                            "name": "foo",
+                            "type": "PRESSURE"
+                        }
+                    }
+                ]
+            }
+        },
+        "execution_layers": [
+            [
+                {
+                    "id": "force.bdss.enthought.plugin.test.v0.factory.probe_data_source",
+                    "model_data": {
+                        "input_slot_info": [
+                            {
+                                "source": "Environment",
+                                "name": "foo"
+                            }
+                        ],
+                        "output_slot_info": [
+                            {
+                                "name": "bar",
+                                "is_kpi": true
+                            }
+                        ]
+                    }
+                }
+            ]
+        ],
+        "notification_listeners": [
+            {
+                "id": "force.bdss.enthought.plugin.test.v0.factory.probe_notification_listener",
+                "model_data": {
+                }
+            }
+        ]
+    }
+}
diff --git a/force_bdss/tests/probe_classes/data_source.py b/force_bdss/tests/probe_classes/data_source.py
index 65340f1df98a4923d1ff3fe2d8d4937423bad2a3..b2f83cbfead608b590e17e9e7dcc06a919b4a71e 100644
--- a/force_bdss/tests/probe_classes/data_source.py
+++ b/force_bdss/tests/probe_classes/data_source.py
@@ -4,10 +4,11 @@ from force_bdss.api import (
     BaseDataSourceFactory, BaseDataSourceModel, BaseDataSource,
     Slot
 )
+from force_bdss.core.data_value import DataValue
 
 
-def run_func(*args, **kwargs):
-    return []
+def run_func(model, parameters):
+    return [DataValue() for _ in range(model.output_slots_size)]
 
 
 class ProbeDataSource(BaseDataSource):
@@ -35,8 +36,8 @@ class ProbeDataSourceModel(BaseDataSourceModel):
     input_slots_type = Str('PRESSURE')
     output_slots_type = Str('PRESSURE')
 
-    input_slots_size = Int(0)
-    output_slots_size = Int(0)
+    input_slots_size = Int(1)
+    output_slots_size = Int(1)
 
     @on_trait_change('input_slots_type,output_slots_type,'
                      'input_slots_size,output_slots_size')
@@ -51,8 +52,8 @@ class ProbeDataSourceFactory(BaseDataSourceFactory):
     input_slots_type = Str('PRESSURE')
     output_slots_type = Str('PRESSURE')
 
-    input_slots_size = Int(0)
-    output_slots_size = Int(0)
+    input_slots_size = Int(1)
+    output_slots_size = Int(1)
 
     raises_on_create_model = Bool(False)
     raises_on_create_data_source = Bool(False)
diff --git a/force_bdss/tests/probe_classes/mco.py b/force_bdss/tests/probe_classes/mco.py
index 905b03cf2e93af290c20d667e6917257d54deccf..1c84b8ee9c350f6df9652fe8136acce8f4cbcb29 100644
--- a/force_bdss/tests/probe_classes/mco.py
+++ b/force_bdss/tests/probe_classes/mco.py
@@ -52,7 +52,7 @@ class ProbeMCOCommunicator(BaseMCOCommunicator):
     send_called = Bool(False)
     receive_called = Bool(False)
 
-    nb_output_data_values = Int(0)
+    nb_output_data_values = Int(1)
 
     def send_to_mco(self, model, kpi_results):
         self.send_called = True
@@ -60,12 +60,13 @@ class ProbeMCOCommunicator(BaseMCOCommunicator):
     def receive_from_mco(self, model):
         self.receive_called = True
         return [
-            DataValue() for _ in range(self.nb_output_data_values)
+            DataValue(name="whatever", value=1.0)
+            for _ in range(self.nb_output_data_values)
         ]
 
 
 class ProbeMCOFactory(BaseMCOFactory):
-    nb_output_data_values = Int(0)
+    nb_output_data_values = Int(1)
 
     raises_on_create_model = Bool(False)
     raises_on_create_optimizer = Bool(False)
diff --git a/force_bdss/tests/test_core_evaluation_driver.py b/force_bdss/tests/test_core_evaluation_driver.py
index b3a0b96b9b014d50dc0d7245e5d0b777c26db410..5d206ecdbce91993263203828b30753d2e84358d 100644
--- a/force_bdss/tests/test_core_evaluation_driver.py
+++ b/force_bdss/tests/test_core_evaluation_driver.py
@@ -38,7 +38,7 @@ class TestCoreEvaluationDriver(unittest.TestCase):
         application.get_plugin = mock.Mock(
             return_value=self.registry
         )
-        application.workflow_filepath = fixtures.get("test_null.json")
+        application.workflow_filepath = fixtures.get("test_probe.json")
         self.mock_application = application
 
     def test_initialization(self):
@@ -49,7 +49,7 @@ class TestCoreEvaluationDriver(unittest.TestCase):
 
     def test_error_for_non_matching_mco_parameters(self):
         mco_factory = self.registry.mco_factories[0]
-        mco_factory.nb_output_data_values = 1
+        mco_factory.nb_output_data_values = 2
         driver = CoreEvaluationDriver(
             application=self.mock_application)
         with testfixtures.LogCapture():
@@ -62,7 +62,7 @@ class TestCoreEvaluationDriver(unittest.TestCase):
     def test_error_for_incorrect_output_slots(self):
 
         def run(self, *args, **kwargs):
-            return [DataValue()]
+            return [DataValue(), DataValue()]
         ds_factory = self.registry.data_source_factories[0]
         ds_factory.run_function = run
         driver = CoreEvaluationDriver(application=self.mock_application)
@@ -70,7 +70,7 @@ class TestCoreEvaluationDriver(unittest.TestCase):
             with six.assertRaisesRegex(
                     self,
                     RuntimeError,
-                    "The number of data values \(1 values\)"
+                    "The number of data values \(2 values\)"
                     " returned by 'test_data_source' does not match"
                     " the number of output slots"):
                 driver.application_started()
@@ -78,11 +78,11 @@ class TestCoreEvaluationDriver(unittest.TestCase):
     def test_error_for_missing_ds_output_names(self):
 
         def run(self, *args, **kwargs):
-            return [DataValue()]
+            return [DataValue(), DataValue()]
 
         ds_factory = self.registry.data_source_factories[0]
         ds_factory.run_function = run
-        ds_factory.output_slots_size = 1
+        ds_factory.output_slots_size = 2
         driver = CoreEvaluationDriver(
             application=self.mock_application,
         )
@@ -90,7 +90,7 @@ class TestCoreEvaluationDriver(unittest.TestCase):
             with six.assertRaisesRegex(
                     self,
                     RuntimeError,
-                    "The number of data values \(1 values\)"
+                    "The number of data values \(2 values\)"
                     " returned by 'test_data_source' does not match"
                     " the number of user-defined names"):
                 driver.application_started()
@@ -323,7 +323,7 @@ class TestCoreEvaluationDriver(unittest.TestCase):
                 ('force_bdss.core_evaluation_driver', 'INFO',
                  'Creating communicator'),
                 ('force_bdss.core_evaluation_driver', 'INFO',
-                 'Received data from MCO: \n'),
+                 'Received data from MCO: \n whatever = 1.0 (AVERAGE)'),
                 ('force_bdss.core_evaluation_driver', 'INFO',
                  'Computing data layer 0'),
                 ('force_bdss.core_evaluation_driver', 'ERROR',
diff --git a/force_bdss/tests/test_core_mco_driver.py b/force_bdss/tests/test_core_mco_driver.py
index 1c09a295c100a65ed2448ada3b145d63bcd2b9d5..abe17a232fe82f69f29b3f92141a793083867e78 100644
--- a/force_bdss/tests/test_core_mco_driver.py
+++ b/force_bdss/tests/test_core_mco_driver.py
@@ -28,7 +28,7 @@ class TestCoreMCODriver(unittest.TestCase):
         application.get_plugin = mock.Mock(
             return_value=self.factory_registry_plugin
         )
-        application.workflow_filepath = fixtures.get("test_null.json")
+        application.workflow_filepath = fixtures.get("test_probe.json")
         self.mock_application = application
 
     def test_initialization(self):