Fix User::avatar_url + add Id display tests

User::avatar_url was formatting the user's Id as a mention, rather than
the inner u64.

src/model/user.rs

@@ -37,7 +37,7 @@ impl CurrentUser {
     /// Returns the formatted URL of the user's icon, if one exists.
     pub fn avatar_url(&self) -> Option<String> {
         self.avatar.as_ref().map(|av|
-            format!(cdn!("/avatars/{}/{}.jpg"), self.id, av))
+            format!(cdn!("/avatars/{}/{}.jpg"), self.id.0, av))
     }
 
     /// Edits the current user's profile settings.
@@ -101,7 +101,7 @@ impl User {
     /// Returns the formatted URL of the user's icon, if one exists.
     pub fn avatar_url(&self) -> Option<String> {
         self.avatar.as_ref().map(|av|
-            format!(cdn!("/avatars/{}/{}.jpg"), self.id, av))
+            format!(cdn!("/avatars/{}/{}.jpg"), self.id.0, av))
     }
 
     /// Gets user as `Member` of a guild.

tests/test_formatters.rs

@@ -0,0 +1,12 @@
+extern crate serenity;
+
+use serenity::model::*;
+
+#[test]
+fn test_formatters() {
+    assert_eq!(format!("{}", ChannelId(1)), "<#1>");
+    assert_eq!(format!("{}", EmojiId(2)), "2");
+    assert_eq!(format!("{}", GuildId(3)), "3");
+    assert_eq!(format!("{}", RoleId(4)), "<@&4>");
+    assert_eq!(format!("{}", UserId(5)), "<@5>");
+}

tests/test_user.rs

@@ -0,0 +1,24 @@
+extern crate serenity;
+
+use serenity::model::{User, UserId};
+
+fn gen() -> User {
+    User {
+        id: UserId(210),
+        avatar: Some("abc".to_owned()),
+        bot: true,
+        discriminator: "1432".to_owned(),
+        name: "test".to_owned(),
+    }
+}
+
+#[test]
+fn test_core() {
+    let mut user = gen();
+
+    assert!(user.avatar_url().unwrap().ends_with("/avatars/210/abc.jpg"));
+
+    user.avatar = None;
+
+    assert!(user.avatar_url().is_none());
+}