merge() with a leading join() doesn't overwrite

[jaads]

I'm trying to load configuration variables from various sources using figment. The module looks like this:

#[derive(Deserialize)]
pub struct Config {
    pub port: u16,
    pub host: String,
}

pub fn load_config() -> Config {
    let file_name = "config";

    Figment::new()
        .join(("port", 8080))
        .join(("host", "localhost"))
        .merge(Env::raw())
        .extract()
        .expect("Fail to load config")
}

When I'm tried to test the load_condig function, it seems that the environment variables don't get loaded. Here is my test module

#[cfg(test)]
mod tests {
    use super::*;
    use std::env;

    #[test]
    fn loads_defaults() {
        let res = load_config();
        assert_eq!(res.host, "localhost");
        assert_eq!(res.port, 8080);
    }

    #[test]
    fn environment_variables_override_defaults() {
        env::set_var("port", "8888");
        let res = load_config();
        assert_eq!(res.port, 8888);
    }
}

The first test run successfully. But the second test fails - the port stays unchanged although I expected it to be overwritten in the figment with 8888.

What I am doing wrong? It seems that the env vars don't get loaded or not overwritten correctly. I also tested with Jail as follows, but with the same result with the port variables don't get overwritten.

#[test]
  fn environment_variables_override_defaults_in_jail() {
      figment::Jail::expect_with(|jail| {
          jail.set_env("port", 8888);
          let res = load_config();
          assert_eq!(res.port, 8888);
          Ok(())
      });
  }

[jaads]

I also wanted to load configuration variables from a file which should overwrite the defaults. But this doesn't seem to work either, although I basically used this example from the docs.

so I think the merge function does not work as expected.

here is a test which is failing:

  #[test]
    fn file_overwrites_defaults_with_jail() {

  #[derive(Debug, Deserialize, PartialEq)]
        pub struct Config {
            pub port: u16,
        }

        figment::Jail::expect_with(|jail| {
            jail.create_file("config.toml", r#"
        port = 9999
    "#)?;

            let config: Config = Figment::new()
                .join(("port", 8080))
                .merge(Toml::file("config.toml"))
                .extract().expect("extract result");

            assert_eq!(config, Config {
                port: 9999,
            });

            Ok(())
        });
    }

why is the port not overwritten by merge() with the value 9999?