Introduce admin and moderator role, check role on list_users action

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

Add test for guards

test/mobilizon/users/service/tools.exs

@@ -0,0 +1,28 @@
+defmodule Mobilizon.Users.Service.ToolsTest do
+  use Mobilizon.DataCase
+
+  import Mobilizon.Factory
+
+  setup do
+    user = insert(:user)
+    moderator = insert(:user, role: :moderator)
+    administrator = insert(:user, role: :administrator)
+    {:ok, user: user, moderator: moderator, administrator: administrator}
+  end
+
+  describe "test guards" do
+    import Mobilizon.Users.Guards
+
+    test "is_moderator/1 guard", %{user: user, moderator: moderator, administrator: administrator} do
+      refute is_moderator(user.role)
+      assert is_moderator(moderator.role)
+      assert is_moderator(administrator.role)
+    end
+
+    test "is_admin/1 guard", %{user: user, moderator: moderator, administrator: administrator} do
+      refute is_admin(user.role)
+      refute is_admin(moderator.role)
+      assert is_admin(administrator.role)
+    end
+  end
+end