Testing Your Config

Two pieces of the crate are shaped for tests; both are described in full in their own chapters, and the testing example shows them together.

Pin configuration with the override layer

Overrides win over everything, which is what makes them useful in tests and behind a --set key=value flag:

#![allow(unused)]
fn main() {
DbConfig::set_override("host", "localhost")?;  // a test, or --set
DbConfig::clear_overrides();
}

A test that sets an override does not care what is in the files, the environment or a remote store — the override outranks all of them. See Sources & Precedence for where the layer sits.

Scope the watcher to the test

start_watch() returns a handle, and dropping it stops the watcher. A server calls .detach() to watch for the rest of the process; anything with a lifecycle — a test, a library, a subcommand — binds the handle so watching stops when the thing being configured goes away:

#![allow(unused)]
fn main() {
let _watch = Config::start_watch()?;   // a test, a subcommand: stop with the scope
}

A second start_watch() while one runs is AlreadyExists, so tests that share a config type should share a watcher or scope each one. See Hot Reload & Watching.