test: add tests for smtp mailer config

test/mv/mailer_test.exs

@@ -0,0 +1,46 @@
+defmodule Mv.MailerTest do
+  @moduledoc """
+  Unit tests for Mv.Mailer, in particular send_test_email/1.
+
+  Uses Swoosh.Adapters.Test (configured in test.exs); no real SMTP. Asserts
+  success/error contract and that one test email is sent on success.
+  """
+  use Mv.DataCase, async: true
+
+  import Swoosh.TestAssertions
+
+  alias Mv.Mailer
+
+  describe "send_test_email/1" do
+    test "returns {:ok, email} and sends one email with expected subject/body when successful" do
+      to_email = "test-#{System.unique_integer([:positive])}@example.com"
+
+      assert {:ok, _email} = Mailer.send_test_email(to_email)
+
+      assert_email_sent(fn email ->
+        to_addresses = Enum.map(email.to, &elem(&1, 1))
+        subject = email.subject || ""
+        body = email.html_body || email.text_body || ""
+
+        to_email in to_addresses and
+          (String.contains?(subject, "Test") or String.contains?(body, "test"))
+      end)
+    end
+
+    test "returns {:error, reason} for invalid email address" do
+      result = Mailer.send_test_email("not-an-email")
+      assert {:error, _reason} = result
+    end
+
+    test "uses mail_from as sender" do
+      to_email = "recipient-#{System.unique_integer([:positive])}@example.com"
+      assert {:ok, _} = Mailer.send_test_email(to_email)
+
+      assert_email_sent(fn email ->
+        {_name, from_email} = Mailer.mail_from()
+        from_addresses = Enum.map(email.from, &elem(&1, 1))
+        from_email in from_addresses
+      end)
+    end
+  end
+end