Implement simple user creation system

Assets/Common/Tests/TestUserCreationScreen.cs

@@ -0,0 +1,29 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+
+public class TestUserCreationScreen : MonoBehaviour
+{
+    void Start()
+    {
+        TestIsValidUsernameTrue();
+        TestIsValidUsernameFalse();
+    }
+
+    public void TestIsValidUsernameTrue()
+    {
+        foreach (char c in "abcdefghijklmnopqrstuvwxyz")
+            Debug.Assert(UserCreationScreen.IsValidUsername(c.ToString()));
+
+        Debug.Assert(UserCreationScreen.IsValidUsername("abcdefghijkl"));
+    }
+
+    public void TestIsValidUsernameFalse()
+    {
+        Debug.Assert(!UserCreationScreen.IsValidUsername(string.Empty));
+        foreach (char c in " \n\t0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ+-*/%_(){}[]\\")
+            Debug.Assert(!UserCreationScreen.IsValidUsername(c.ToString()));
+
+        Debug.Assert(!UserCreationScreen.IsValidUsername("abcdefghijklmnopqrstuvwxyz"));
+    }
+}