def test_get_vertex():
"""Check if vertex can be retrieved from directed graph."""
g = DirectedGraph()
g.add_vertex(vertex_props=None)
v = g.get_vertex(vertex_id=0)
assert v is not None
assert v.id == 0
def test_get_vertex():
g = DirectedGraph()
g.add_vertex(vertex_props=None)
v = g.get_vertex(vertex_id=0)
assert v is not None
def test_get_nonexistent_vertex():
"""Check if non existent vertex can not be retrieved from directed graph."""
g = DirectedGraph()
g.add_vertex(vertex_props=None)
v = g.get_vertex(vertex_id=42)
assert v is None