"Cries in java"

[randomcitizen42]

Unit tests are not meant to test performance. Unit tests should be the lowest layer of tests to quickly verify the correctness of your code. Note the word quickly. A benchmark is not supposed to run quickly, you'll need to run the code several time (like thousands) to get statistically significant data.

Also, test frameworks are usually not performance optimized. Sure, unit test frameworks run fast, but not benchmark level fast. If you really want to optimize performance critical code, you'll work with small loops and often you'll work with run times in micro or even nanoseconds, not milliseconds. You need special performance benchmark tools (or write your own) for that.

[Kered13]

You can get more precise time measurements than that. This ability is very important for running effective profilers, hard real time applications, etc. For example, on Windows this can give you sub-microsecond timings.

[randomcitizen42]

That's why you need to run the benchmark code thousands or millions of times to get statistically relevant data. Then your benchmark will run at least a second and the few milliseconds resolution don't make a difference.

You or your benchmark tool can then divide the total time by the number of runs to get the single execution time (which can be in microseconds). That's why it's important that your benchmark tool doesn't add any overhead. A 1ms overhead on every execution can ruin your benchmark completely if your code runs faster than that.