Repository: paritytech/substrate
File: utils/frame/try-runtime/cli/tests/create_snapshot.rs (Rust)

Code before:
		common::run_with_timeout(Duration::from_secs(60), async move {
			fn create_snapshot(ws_url: &str) -> Child {
				Command::new(cargo_bin("substrate"))
					.stdout(process::Stdio::piped())
					.stderr(process::Stdio::piped())
					.args(&["try-runtime", "--runtime=existing"])
					.args(&["create-snapshot", format!("--uri={}", ws_url).as_str()])
					.kill_on_drop(true)
					.spawn()
					.unwrap()
			}

			// Start a node and wait for it to begin finalizing blocks
			let mut node = common::KillChildOnDrop(common::start_node());
			let ws_url = common::extract_info_from_output(node.stderr.take().unwrap()).0.ws_url;
			common::wait_n_finalized_blocks(1, &ws_url).await;

			// Try to create a snapshot.
			let mut snapshot_creation = create_snapshot(&ws_url);
			let re = Regex::new(r#".*writing snapshot of (\d+) bytes to .*"#).unwrap();
			let matched =
				common::wait_for_stream_pattern_match(snapshot_creation.stderr.take().unwrap(), re)
					.await;

			// Assert that the snapshot creation succeded.
			assert!(matched.is_ok());

			let snapshot = fs::read_dir(".")
				.expect("Failed to read the current directory")
				.filter_map(Result::ok)
				.find(|entry| {
					entry.path().is_file() &&
						entry.path().extension().map(|ext| ext == "snap").unwrap_or(false)
				});

			assert!(snapshot.is_some());
		})
		.await;
	}
}


Review comment (bug):
```suggestion
			assert!(matched.is_ok(), "Failed to create snapshot");
```

Code after:
#[tokio::test]
async fn create_snapshot_works() {
	// Build substrate so binaries used in the test use the latest code.
	common::build_substrate(&["--features=try-runtime"]);

	let temp_dir = tempfile::Builder::new()
		.prefix("try-runtime-cli-test-dir")
		.tempdir()
		.expect("Failed to create a tempdir");
	let snap_file_path = temp_dir.path().join("snapshot.snap");

	common::run_with_timeout(Duration::from_secs(60), async move {
		fn create_snapshot(ws_url: &str, snap_file: &PathBuf, at: Hash) -> Child {
			Command::new(cargo_bin("substrate"))
				.stdout(process::Stdio::piped())
				.stderr(process::Stdio::piped())
				.args(&["try-runtime", "--runtime=existing"])
				.args(&["create-snapshot", format!("--uri={}", ws_url).as_str()])
				.arg(snap_file)
				.args(&["--at", format!("{:?}", at).as_str()])
				.kill_on_drop(true)
				.spawn()
				.unwrap()
		}

		// Start a node and wait for it to begin finalizing blocks
		let mut node = common::KillChildOnDrop(common::start_node());
		let ws_url = common::extract_info_from_output(node.stderr.take().unwrap()).0.ws_url;
		common::wait_n_finalized_blocks(3, &ws_url).await;

		let block_number = 2;
		let block_hash = common::block_hash(block_number, &ws_url).await.unwrap();

		// Try to create a snapshot.
		let mut snapshot_creation = create_snapshot(&ws_url, &snap_file_path, block_hash);

		let re = Regex::new(r#".*writing snapshot of (\d+) bytes to .*"#).unwrap();
		let matched =
			common::wait_for_stream_pattern_match(snapshot_creation.stderr.take().unwrap(), re)
				.await;

		// Assert that the snapshot creation succeded.
		assert!(matched.is_ok(), "Failed to create snapshot");

		let snapshot_is_on_disk = Path::new(&snap_file_path).exists();
		assert!(snapshot_is_on_disk, "Snapshot was not written to disk");

		// Try and load the snapshot we have created by running `create-snapshot`.
		let snapshot_loading_result = Builder::<Block>::new()
			.mode(Mode::Offline(OfflineConfig {
				state_snapshot: SnapshotConfig { path: snap_file_path },