Looks like if you run cargo test using nightly you can print times at least if you allow unstable options
$ cargo test -- --report-time
Finished test [unoptimized + debuginfo] target(s) in 0.69s
Running unittests src/lib.rs (target/debug/deps/cache-0f6452d8f8bdc1b1)
error: The "report-time" flag is only accepted on the nightly compiler with -Z unstable-options
But actually, you don't need nightly. Just use unstable options, as in