Consider the following code:

fn main() {
    use std::alloc::{alloc, dealloc, Layout};
    unsafe {
        let ptr = alloc(Layout::from_size_align(4096, 4096).unwrap());
        dealloc(ptr, Layout::from_size_align(4096, 1).unwrap());
    }
}

Yes, it breaks the invariants for dealloc, and yes, it crashes on Windows, with:

error: process didn't exit successfully: `target/debug/foo.exe` (exit code: 0xc0000374, STATUS_HEAP_CORRUPTION)

The problem is that when that happens in a test, the test just fails in a completely non-useful manner. (just switch to a lib crate, rename the function and add #[test]).

The test fails with:

running 1 test
error: test failed, to rerun pass '--lib'

And nothing else.
When the crate happens to have other tests, some other tests, but not all, will show test foo... ok, then the same error.