rest: remove specification validate from "create" endpoint

- because client doesn't include Yadage specification in "create" endpoint, validation fails;
- workflow validation is moved to "start_workflow" so in case Yadage specification has multiple files, they can be loaded and properly validated.

closes reanahub#535

reana_server/rest/workflows.py

@@ -525,9 +525,6 @@ def create_workflow(user):  # noqa
         if is_uuid_v4(workflow_name):
             return jsonify({"message": "Workflow name cannot be a valid UUIDv4."}), 400
 
-        validate_workflow(reana_spec_file, input_parameters={})
-        workspace_root_path = reana_spec_file.get("workspace", {}).get("root_path")
-
         workflow_engine = reana_spec_file["workflow"]["type"]
         if workflow_engine not in REANA_WORKFLOW_ENGINES:
             raise Exception("Unknown workflow type.")
@@ -536,6 +533,9 @@ def create_workflow(user):  # noqa
             workflow_engine, reana_spec_file.get("inputs", {}).get("options", {})
         )
 
+        workspace_root_path = reana_spec_file.get("workspace", {}).get("root_path")
+        validate_workspace_path(reana_spec_file)
+
         retention_days = reana_spec_file.get("workspace", {}).get("retention_days")
         retention_rules = get_workspace_retention_rules(retention_days)
 
@@ -1230,6 +1230,12 @@ def start_workflow(workflow_id_or_name, user):  # noqa
             )
         if "yadage" in (workflow.type_, restart_type):
             _load_and_save_yadage_spec(workflow, operational_options)
+
+        input_parameters = parameters.get("input_parameters", {})
+        validate_workflow(
+            workflow.reana_specification, input_parameters=input_parameters
+        )
+
         publish_workflow_submission(workflow, user.id_, parameters)
         response = {
             "message": "Workflow submitted.",

tests/test_views.py

@@ -134,7 +134,7 @@ def test_create_workflow(
             )
             assert res.status_code == 400
 
-            # not valid specification
+            # not valid specification. but there is no validation
             workflow_specification = {
                 "workflow": {"specification": {}, "type": "serial"},
             }
@@ -147,7 +147,7 @@ def test_create_workflow(
                 },
                 data=json.dumps(workflow_specification),
             )
-            assert res.status_code == 400
+            assert res.status_code == 200
 
             # correct case
             workflow_specification = sample_serial_workflow_in_db.reana_specification
@@ -163,6 +163,33 @@ def test_create_workflow(
             assert res.status_code == 200
 
 
+def test_start_workflow_validates_specification(
+    app, session, default_user, sample_serial_workflow_in_db
+):
+    with app.test_client() as client:
+        sample_serial_workflow_in_db.status = RunStatus.created
+        sample_serial_workflow_in_db.name = "test"
+        session.add(sample_serial_workflow_in_db)
+        session.commit()
+
+        workflow_specification = copy.deepcopy(
+            sample_serial_workflow_in_db.reana_specification
+        )
+        workflow_specification["workflow"]["steps"] = "unknown"
+        body = {
+            "reana_specification": workflow_specification,
+        }
+        res = client.post(
+            url_for("workflows.start_workflow", workflow_id_or_name="test"),
+            headers={"Content-Type": "application/json"},
+            query_string={
+                "access_token": default_user.access_token,
+            },
+            data=json.dumps(body),
+        )
+        assert res.status_code == 400
+
+
 def test_restart_workflow_validates_specification(
     app, session, default_user, sample_serial_workflow_in_db
 ):