2 releases
0.1.1 | Oct 28, 2024 |
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0.1.0 | Feb 6, 2023 |
#121 in Testing
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env_wrapper
A wrapper around the standard std::env
functions that allows for a test double to be injected during testing.
Limitations
At this time, this crate only works for Unix-like systems.
Motivation
Testing code that relies on the state of environment variables can be fragile, since the state may change between tests or be polluted by other tests. The ideal solution is to have a private set of environment variables per test, so these problems cannot happen.
Approach
This crate introduces the RealEnvironment
(a wrapper around the functions in std::env
)
and
FakeEnvironment
structs, which implement the
Environment
trait. Instead of using
std::env
directly,
use RealEnvironment
with
dependency injection
so each of your tests can have a private set of environment variables.
Example
Scenario: An app looks for the presence of the CONFIG_LOCATION
environment
variable. If it isn't set, it uses a default location.
use env_wrapper::{Environment, RealEnvironment};
const CONFIG_LOCATION_ENV_VAR_NAME: &str = "CONFIG_LOCATION";
const DEFAULT_CONFIG_LOCATION: &str = "/etc/my_app/service.conf";
fn main() {
// In the production code, inject RealEnvironment.
let real_env = RealEnvironment;
let config_location = get_config_location(real_env);
}
fn get_config_location(env: impl Environment) -> String {
match env.var(CONFIG_LOCATION_ENV_VAR_NAME) {
Ok(location) => location,
_ => DEFAULT_CONFIG_LOCATION.to_string(),
}
}
#[test]
fn when_the_user_has_set_the_config_location_env_var_then_use_that_location() {
use env_wrapper::FakeEnvironment;
// Arrange
// Each test should have a separate instance of FakeEnvironment.
let mut fake_env = FakeEnvironment::new();
let user_specified_location = "/a/user/specified/location";
fake_env.set_var(CONFIG_LOCATION_ENV_VAR_NAME, user_specified_location);
// Act
// In the test code, inject FakeEnvironment.
let location = get_config_location(fake_env);
// Assert
assert_eq!(location, user_specified_location);
}
License
Licensed under either of
- Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.
Code of Conduct
All behavior is governed by the Rust Code of Conduct.