test_cofactor = ->
run_test [
"cofactor([[1,2],[3,4]],1,1)",
"4",
"cofactor([[1,2],[3,4]],1,2)",
"-3",
"cofactor([[1,2],[3,4]],2,1)",
"-2",
"cofactor([[1,2],[3,4]],2,2)",
"1",
"cofactor([[1,2,3],[4,5,6],[7,8,9]],1,2)",
"6",
]