The `cargo test` command cannot parallelize across crates and it makes
tests slower than necessary:

```
$ time cargo test --all
...
real	0m8,449s
user	1m24,149s
sys	0m37,558s
```

Comparing with `nextest` the difference is clear:

```
$ time cargo nextest run --all
...
real	0m2,898s
user	0m5,922s
sys	0m2,079s
```

Signed-off-by: Wiktor Kwapisiewicz <wiktor@metacode.biz>