message: add test for headers module.
diff: @@ -232,3 +232,26 @@ impl Spotify {
  self.delete(url, Some(&headers), payload).await
  }
  }
  +
  +mod tests {
  + use super::*;
  + use crate::oauth2::TokenBuilder;
  + #[test]
  + fn test_bearer_auth() {
  + let access_token = "access_token";
  + let tok = TokenBuilder::default()
  + .access_token(access_token)
  + .build()
  + .unwrap();
  + let (auth, value) = headers::bearer_auth(&tok);
  + assert_eq!(auth, "authorization");
  + assert_eq!(value, "Bearer access_token");
  + }
  +
  + #[test]
  + fn test_basic_auth() {
  + let (auth, value) = headers::basic_auth("ramsay", "123456");
  + assert_eq!(auth, "authorization");
  + assert_eq!(value, "Basic cmFtc2F5OjEyMzQ1Ng==");
  + }
  +}
  