Add test and

DCO Remediation Commit for Thijs Baaijen <[email protected]>

I, Thijs Baaijen <[email protected]>, hereby add my Signed-off-by to this commit: b1601a8
I, Thijs Baaijen <[email protected]>, hereby add my Signed-off-by to this commit: 0598eb8
I, Thijs Baaijen <[email protected]>, hereby add my Signed-off-by to this commit: 82d52f9

Signed-off-by: Thijs Baaijen <[email protected]>

Author: Thijss

tests/unit/model/graphs/test_graph_model.py

@@ -10,6 +10,7 @@
 import pytest
 from numpy.testing import assert_array_equal
 
+from power_grid_model_ds._core.model.graphs.errors import GraphError
 from power_grid_model_ds._core.model.graphs.models.base import BaseGraphModel
 from power_grid_model_ds._core.model.grids.base import Grid
 from power_grid_model_ds.errors import MissingBranchError, MissingNodeError, NoPathBetweenNodes
@@ -30,6 +31,11 @@ def test_graph_add_node_and_branch(self, graph: BaseGraphModel):
         assert 2 == graph.nr_nodes
         assert 1 == graph.nr_branches
 
+    def test_add_node_already_there(self, graph: BaseGraphModel):
+        graph.add_node(1)
+        with pytest.raises(GraphError):
+            graph.add_node(1)
+
     def test_add_invalid_branch(self, graph: BaseGraphModel):
         graph.add_node(1)
         graph.add_node(2)