from topo_sort import topo_sort

def check(order, edges):
    pos = {n:i for i,n in enumerate(order)}
    for u,v in edges:
        assert pos[u] < pos[v], (u,v,order)

# DAG basic
order, cyc = topo_sort([1,2,3], [(1,2),(2,3)])
assert cyc is None and order == [1,2,3], (order,cyc)
check(order, [(1,2),(2,3)])

# disconnected
order, cyc = topo_sort([1,2,3,4], [(1,2)])
assert cyc is None and set(order)=={1,2,3,4}
check(order, [(1,2)])

# deterministic tie-break
order, cyc = topo_sort(["b","a","c"], [])
assert order == ["a","b","c"], order

# duplicate edges deduped
order, cyc = topo_sort([1,2], [(1,2),(1,2)])
assert cyc is None and order==[1,2]

# cycle
order, cyc = topo_sort([1,2,3], [(1,2),(2,3),(3,1)])
assert cyc is not None
# verify it's a cycle
s = set(cyc)
assert len(cyc) == len(s)+1 or len(cyc)==len(s), cyc  # cycle list may include repeat? ours no repeat of first? we built v..u no repeat
# check edges close
edgeset = {(1,2),(2,3),(3,1)}
# cycle consecutive
for i in range(len(cyc)):
    a=cyc[i]; b=cyc[(i+1)%len(cyc)]
    assert (a,b) in edgeset, (a,b)
print("cycle:", cyc)

# self loop
order, cyc = topo_sort([1], [(1,1)])
assert cyc == [1], cyc

# unknown node raises
try:
    topo_sort([1], [(1,2)])
    raise SystemExit("expected ValueError")
except ValueError:
    pass

# duplicate node raises
try:
    topo_sort([1,1], [])
    raise SystemExit("expected ValueError")
except ValueError:
    pass

print("ALL TESTS PASSED")