testlist <- list(fpr = structure(c(1.64237420032646e+249, 6.68205076097546e+275,  4.34072562510218e+48, 1.47141116485374e+246, 2.02405564830198e+250 ), .Dim = c(5L, 1L)), n_steps = 256456812L, tpr = structure(c(1.29237345829394e-211,  4.37706376853046e+136, 1.17406306133778e+181, 2.31087215925358e-38,  2.83690277657871e-252, 9.13869605226064e+66, 3.60230257100362e+250,  3.38507256413585e+124, 1.45668716741674e+231, 8.16002560827776e+270,  1.10139258887696e+123, 1.99140635225899e+78, 2.20565515902883e+269,  9.64473847839622e-34, 5.29546398985559e-249, 8.04412997233088e-266 ), .Dim = c(4L, 4L)))
result <- do.call(fbroc:::fpr_at_tpr_cached,testlist)
str(result)