test(vereinfacht): add tests and scope README

- Config, Client, SyncContact, Vereinfacht module tests (no real API)
- vereinfacht_test_README: document test scope

test/mv/vereinfacht/client_test.exs

@@ -0,0 +1,50 @@
+defmodule Mv.Vereinfacht.ClientTest do
+  @moduledoc """
+  Tests for Mv.Vereinfacht.Client.
+
+  Only tests the "not configured" path; no real HTTP calls. Config reads from
+  ENV first, then from Settings (DB), so we use DataCase so get_settings() is available.
+  """
+  use Mv.DataCase, async: false
+
+  alias Mv.Vereinfacht.Client
+
+  setup do
+    clear_vereinfacht_env()
+    :ok
+  end
+
+  describe "create_contact/1" do
+    test "returns {:error, :not_configured} when Vereinfacht is not configured" do
+      member = build_member_struct()
+
+      assert Client.create_contact(member) == {:error, :not_configured}
+    end
+  end
+
+  describe "update_contact/2" do
+    test "returns {:error, :not_configured} when Vereinfacht is not configured" do
+      member = build_member_struct()
+
+      assert Client.update_contact("123", member) == {:error, :not_configured}
+    end
+  end
+
+  defp build_member_struct do
+    %{
+      first_name: "Test",
+      last_name: "User",
+      email: "test@example.com",
+      street: "Street 1",
+      house_number: "2",
+      postal_code: "12345",
+      city: "Berlin"
+    }
+  end
+
+  defp clear_vereinfacht_env do
+    System.delete_env("VEREINFACHT_API_URL")
+    System.delete_env("VEREINFACHT_API_KEY")
+    System.delete_env("VEREINFACHT_CLUB_ID")
+  end
+end