Backup platform impl

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

testing/wasm-tests/tests/wasm.rs

@@ -1,7 +1,9 @@
 #![cfg(target_arch = "wasm32")]
 
 use subxt::config::PolkadotConfig;
+use subxt::rpc::LightClient;
 use wasm_bindgen_test::*;
+use std::sync::Arc;
 
 wasm_bindgen_test::wasm_bindgen_test_configure!(run_in_browser);
 
@@ -16,3 +18,12 @@ async fn wasm_ws_transport_works() {
     let chain = client.rpc().system_chain().await.unwrap();
     assert_eq!(&chain, "Development");
 }
+
+#[wasm_bindgen_test]
+async fn light_client_transport_works() {
+    let light_client = LightClient::new(include_str!("../../artifacts/dev_spec.json")).unwrap();
+    let client = subxt::client::OnlineClient::<PolkadotConfig>::from_rpc_client(Arc::new(light_client)).await.unwrap();
+
+    let chain = client.rpc().system_chain().await.unwrap();
+    assert_eq!(&chain, "Development");
+}