improve usernames

test/user/user_test.dart

@@ -5,6 +5,7 @@ void main() {
   validUsernameTest();
   usernameToUrlTest();
   cleanupNameTest();
+  userFromUsernameTest();
 }
 
 void validUsernameTest() {
@@ -36,3 +37,10 @@ void cleanupNameTest() {
     expect(cleanUpUsername(name: ""), "");
   });
 }
+
+void userFromUsernameTest() {
+  test("try extracting user from the full valid user id", () {
+    expect(userFromUsername(name: "@hello@world"), "hello");
+    expect(userFromUsername(name: "@john@from.garfield"), "john");
+  });
+}