integration: add tests for hostname resolution

Two scenarios are tested:
1) when some hostnames are invalid, but there are some addresses
   resolved successfully, initialisation continues without an error,
2) when all hostnames are invalid, and there are no adresses given,
   then NewSessionError::FailedToResolveAnyHostname is returned.

scylla/tests/integration/main.rs

@@ -1,5 +1,6 @@
 mod execution_profiles;
 mod hygiene;
 mod lwt_optimisation;
+mod new_session;
 mod retries;
 pub(crate) mod utils;

scylla/tests/integration/new_session.rs

@@ -0,0 +1,34 @@
+use assert_matches::assert_matches;
+use scylla::SessionBuilder;
+use scylla_cql::errors::NewSessionError;
+
+#[cfg(not(scylla_cloud_tests))]
+#[tokio::test]
+async fn proceed_if_only_some_hostnames_are_invalid() {
+    // on purpose left without port
+    let uri1 = "scylladbisthefastest.db".to_owned();
+    // correctly provided port, but unknown domain
+    let uri2 = "cassandrasuckssomu.ch:9042".to_owned();
+    let uri3 = std::env::var("SCYLLA_URI3").unwrap_or_else(|_| "127.0.0.3:9042".to_string());
+
+    let session = SessionBuilder::new()
+        .known_nodes([uri1, uri2, uri3])
+        .build()
+        .await
+        .unwrap();
+    session
+        .query("SELECT host_id FROM system.local", &[])
+        .await
+        .unwrap();
+}
+
+#[cfg(not(scylla_cloud_tests))]
+#[tokio::test]
+async fn all_hostnames_invalid() {
+    let uri = "cassandrasuckssomu.ch:9042".to_owned();
+
+    assert_matches!(
+        SessionBuilder::new().known_node(uri).build().await,
+        Err(NewSessionError::FailedToResolveAnyHostname(_))
+    );
+}