temp-env

Set environment variables temporarily.

This crate is useful for testing with different environment variables that should not interfere when running cargo test.

This code started as a small test helper written by @fabian-braun and @nbaztec and published by @fabian-braun on StackOverflow. @vmx found it useful and took the time to make it a proper crate.

Examples

temp_env::with_var("MY_ENV_VAR", Some("production"), || {
    // Run some code where `MY_ENV_VAR` is set to `production`.
});


temp_env::with_vars(
    [
        ("FIRST", Some("Hello")),
        ("SECOND", Some("World!")),
    ],
    || {
        // Run some code where `FIRST` is set to `Hello` and `SECOND` is set to `World!`.
    }
);

temp_env::with_vars(
    [
        ("FIRST", Some("Hello")),
        ("SECOND", None),
    ],
    || {
        // Run some code where `FIRST` is set to `Hello` and `SECOND` is unset (even if
        // it was set before)
    }
);

let value = temp_env::with_var("MY_ENV_VAR", Some("production"), || {
    // Compute a value in a closure while `MY_ENV_VAR` is set to `production`.
    let envvar = env::var("MY_ENV_VAR").unwrap();
    if envvar == "production" {
        true
    } else {
        false
    }
});

How does it work?

This crate sets and unsets environment variables for the currently running (Rust) process. It leverages std::env::set_var.

The provided functions temp_env::with_* provide the following features:

• Avoid interference when running concurrently
• Reset previously set env variables back to their original value upon completion, also in case of panic
• Temporarily unsetting env variables

Note that the crate makes use of a singleton mutex to avoid side effects between concurrently running tests. This may impact the degree of concurrency in your test execution.

Features

• async_closure: When enabled you can use async_with_var() with async closures. This feature needs at least Rust version 1.64.

Noteworthy

As an alternative to using this crate, you might consider migrating your testing to cargo-nextest. cargo-nextest runs each test in a separate process, which makes it unnecessary to synchronize the altering of environment variables as described here.

License

This project is licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE) or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.