ordered jobs kata in erlang

jobsort.erl

-module (jobsort).
 
-export ([sort/1,test/0]).
 
sort(JobSpec) ->
	EdgesAndVertices = get_edges_and_vertices(string:tokens(JobSpec, "\r\n"), [], []),
	Graph = build_graph(EdgesAndVertices),
	case digraph_utils:is_acyclic(Graph) of
		true ->
			lists:reverse(digraph_utils:topsort(Graph));
		false ->
			"jobs list contains cyclic dependancy"
	end.
 
build_graph({Vertices,Edges}) ->
	Graph = digraph:new(),
	lists:foldl(fun (V,_) -> digraph:add_vertex(Graph, V) end, [], Vertices),
	lists:foldl(fun ({E1,E2},_) -> digraph:add_edge(Graph,E1,E2) end, [], Edges),
	Graph.
 
get_edges_and_vertices([], Vertices, Edges) ->
	{lists:usort(Vertices), Edges};
get_edges_and_vertices([Job|OtherJobs], Vertices, Edges) ->
	case string:tokens(Job, " ") of
		[Dependant, _, Dependancy] ->
			get_edges_and_vertices(OtherJobs, [Dependant, Dependancy | Vertices], [{Dependant,Dependancy} | Edges]);
		[Vertex,_] ->
			get_edges_and_vertices(OtherJobs, [Vertex | Vertices],Edges)
	end.

test() ->
	%1 no jobs, empty result
	[] = sort(""),
	%2 single job, no dependancy
	["a"] = sort("a ->"),
	%3 multiple single jobs, no dependancies
	["a","c","b"] = sort("a ->\r\nb ->\r\nc ->"),
	%4 single job with dependancies
	["b","a"] = sort("a -> b"),
	%5 multiple jobs with dependancies
	["c","b","a","e","d","f"] = sort("a -> b\r\nb -> c\r\nd -> e\r\nf -> a"),
	%6 self dependancy
	"jobs list contains cyclic dependancy" = sort("a -> a"),
	%6 cyclic dependancy
	"jobs list contains cyclic dependancy" = sort("a -> b\r\nb -> c\r\nc -> a"),
	%7 multiple dependancies \ dependants
	["b","d","c","a","f"] = sort("a -> b\r\na -> c\r\nc -> d\r\nf -> c"),
	"tests passed".