Function config_env 

pub fn config_env<P: ConfigProvider + 'static>(provider: P) -> ConfigEnv

Build a minimal ConfigEnv wrapping provider.

use std::sync::Arc;
use effect_config::{Config, MapConfigProvider, config_env, ConfigError};
use id_effect::run_blocking;

let p = MapConfigProvider::from_pairs([("HOST", "localhost")]);
let host: String = run_blocking(
  Config::string("HOST").run::<String, ConfigError, _>(),
  config_env(p),
)
.unwrap();
assert_eq!(host, "localhost");