def test_get_vertices_graph_with_one_vertex():
"""Test whether method DirectedGraph.get_vertices() works correctly."""
g = DirectedGraph()
v0 = g.add_vertex(vertex_props=None)
list_vertices = g.get_vertices()
assert len(list_vertices) == 1
assert v0 in list_vertices
def test_get_vertices():
g = DirectedGraph()
v0 = g.add_vertex(vertex_props=None)
v1 = g.add_vertex(vertex_props=None)
list_vertices = g.get_vertices()
assert len(list_vertices) == 2
assert v0 in list_vertices
assert v1 in list_vertices
def test_get_vertices_empty_graph():
"""Test whether method DirectedGraph.get_vertices() works correctly for empty graph."""
g = DirectedGraph()
list_vertices = g.get_vertices()
assert not list_vertices