We have only partial coverage for our tracing API. Specially I am concerned the methods that are useful only when something goes wrong, e.g. debug_standardTraceBlockToFile, debug_standardTraceBadBlockToFile, debug_intermediateRoots are out of date and we might find ourselves not being able to use them when they are needed. We have some tests in eth/tracers/api_test.go. We should expand them to cover at least these 3 methods + debug_traceBadBlock.