Test empty graph and graph with no edges

Author: cmalinmayor

tests/test_solver.py

@@ -0,0 +1,49 @@
+import motile
+import networkx as nx
+from motile.costs import EdgeSelection, NodeSelection
+
+
+def test_empty_graph() -> None:
+    """Test that solving an empty graph does not error and returns empty solution."""
+    nx_graph = nx.DiGraph()
+    graph = motile.TrackGraph(nx_graph)
+
+    solver = motile.Solver(graph)
+    solver.add_cost(NodeSelection(constant=-1))
+    solver.add_cost(EdgeSelection(constant=-1))
+
+    # Should not error
+    solver.solve()
+    solution_graph = solver.get_selected_subgraph()
+
+    # Solution should be empty
+    assert len(solution_graph.nodes) == 0
+    assert len(solution_graph.edges) == 0
+
+
+def test_graph_with_no_edges() -> None:
+    """Test that solving a graph with nodes but no edges does not error."""
+    cells = [
+        {"id": 0, "t": 0},
+        {"id": 1, "t": 0},
+        {"id": 2, "t": 1},
+    ]
+
+    nx_graph = nx.DiGraph()
+    nx_graph.add_nodes_from([(cell["id"], cell) for cell in cells])
+    # No edges added
+
+    graph = motile.TrackGraph(nx_graph)
+
+    solver = motile.Solver(graph)
+    solver.add_cost(NodeSelection(constant=-1))
+    solver.add_cost(EdgeSelection(constant=-1))
+
+    # Should not error
+    solver.solve()
+    solution_graph = solver.get_selected_subgraph()
+
+    # All nodes should be selected due to negative cost
+    assert set(solution_graph.nodes.keys()) == {0, 1, 2}
+    # No edges should be selected (none exist)
+    assert len(solution_graph.edges) == 0