tests: add integration test

build.sbt

@@ -105,4 +105,13 @@ lazy val courier = (project in file("courier"))
       "org.jvnet.mock-javamail" % "mock-javamail" % "1.9" % Test
     ),
     testFrameworks += new TestFramework("munit.Framework")
-  )
+  )
+lazy val it = (project in file("integration-tests"))
+  .settings(commonSettings ++ cFlags)
+  .settings(
+    name := "courier-integration-tests",
+    libraryDependencies ++= Seq(
+      "org.scalameta"     %% "munit"          % "0.7.27" % Test,
+    ),
+    testFrameworks += new TestFramework("munit.Framework")
+  ).dependsOn(courier)

integration-tests/src/test/scala/mailspec.scala

@@ -0,0 +1,23 @@
+package courier
+
+import scala.concurrent.Await
+import scala.concurrent.ExecutionContext.Implicits.global
+import scala.concurrent.duration._
+
+
+class MailSpec extends munit.FunSuite {
+  test("the mailer should send an email") {
+    assume(sys.env("CI").isEmpty(), "This test is meant to be ran locally.")
+    val email = sys.env("IT_EMAIL")
+    val password = sys.env("IT_PASSWORD")
+    val mailer = Mailer("smtp.gmail.com", 587)
+                .auth(true)
+                .as(email, password)
+                .startTls(true)()
+    val mId = Await.result(mailer(Envelope.from(email.addr)
+            .to(email.addr)
+            .subject("miss you")
+            .content(Text("hi mom"))), 10.seconds)
+    assert(mId.nonEmpty, "Message-ID should be set by the Transport.send call")
+  }
+}