Chaotic testing harness

Kaos is a chaotic testing harness to test your services against random failures. It allows you to add points to your code to crash sporadically and harness asserts availability and fault tolerance of your services by seeking minimum time between failures, fail points, and randomized runs.

Kaos is equivalent of Chaos Monkey for the Rust ecosystem. But it is more smart to find the closest MTBF based on previous runs. This is dependable system practice. For more information please visit Chaos engineering.

Test Setup

It is better to separate resilience tests. Create a directory that will hold all chaos tests. In our example it will be kaos-tests.

A minimal launcher for kaos setup looks like this:

#[test]
fn chaos_tests() {
let k = kaos::Runs::new();

for entry in fs::read_dir("kaos-tests").unwrap() {
let entry = entry.unwrap();
let path = entry.path();

// Every service run should be available at least 2 seconds
k.available(path, Duration::from_secs(2));
}
}

and in your Cargo.toml

[[test]]
name = "chaos_tests"
path = "kaos-tests/launcher.rs"

Definining flunks

In kaos there is a concept of [flunk]. Every flunk is a point of failure with panic. This can be redefinable. After adding kaos as dependency you can add flunk points to define fallible operations or crucial points that system should continue its operation.

Basic flunk is like:

use kaos::flunk;
fn vec_check(v: &Vec<usize>) {
if v.len() == 3 {
flunk!("fail-when-three-elems");
}
}

This flunk point will be used later by kaos.

Writing tests

Test harness will execute tests marked by a launcher. An example test for the flunk mentioned above is like this:

# use std::panic;
# use kaos::flunk;
# fn vec_check(v: &Vec<usize>) {
#   if v.len() == 3 {
#     flunk!("fail-when-three-elems");
#   }
# }
use kaos::kaostest;

kaostest!("fail-when-three-elems",
{
panic::catch_unwind(|| {
let mut v = &mut vec![];
loop {
v.push(1);
vec_check(v);
}
});
}
);

That's all, now what you have to do is run with cargo test.

Kaos is using the same approach that trybuild has. Instead of being compiler-like test harness, it has diverged to be chaos engineering oriented harness.