def test_simple_has_cycle_start_off_1():
d = graph.Node()
c = graph.Node(next_node = d)
b = graph.Node(next_node = c)
d.next = b
a = graph.Node(next_node = b)
assert graph.has_cycle(a)
def test_simple_has_cycle_start_off_2():
e = graph.Node()
d = graph.Node(next_node = e)
c = graph.Node(next_node = d)
b = graph.Node(next_node = c)
e.next = b
a = graph.Node(next_node = b)
assert graph.has_cycle(a)
def test_no_cycles_simple():
b = graph.Node()
a = graph.Node(next_node=b)
assert not graph.has_cycle(a)
def test_empty_has_no_cycles_single_node():
a = graph.Node()
assert not graph.has_cycle(a)
def test_empty_has_no_cycles():
assert not graph.has_cycle(None)
def test_simple_has_cycle():
b = graph.Node()
a = graph.Node(next_node = b)
b.next = a
assert graph.has_cycle(a)
def test_single_node_cycle():
a = graph.Node()
a.next = a
assert graph.has_cycle(a)