Off-chain Worker Test Environment

Learn more about how to set up and use offchain-workers in the offchain-demo entree.

Mock Runtime Setup

In addition to everything we need to set up in Basic Test Environment, we also need to set up the mock for SubmitTransaction, and implement the CreateTransaction trait for the runtime.

src: pallets/offchain-demo/src/

fn main() {
type TestExtrinsic = TestXt<Call<TestRuntime>, ()>;
type SubmitTransaction = system::offchain::TransactionSubmitter<

impl Trait for TestRuntime {
	// ...snip
	// For signed transaction
	type SubmitSignedTransaction = SubmitTransaction;
	// For unsigned transaction
	type SubmitUnsignedTransaction = SubmitTransaction;

impl system::offchain::CreateTransaction<TestRuntime, TestExtrinsic> for TestRuntime {
	type Public = sr25519::Public;
	type Signature = sr25519::Signature;

	fn create_transaction<TSigner: system::offchain::Signer<Self::Public, Self::Signature>> (
		call: Call<TestRuntime>,
		public: Self::Public,
		_account: <TestRuntime as system::Trait>::AccountId,
		index: <TestRuntime as system::Trait>::Index,
	) -> Option<(Call<TestRuntime>, <TestExtrinsic as sp_runtime::traits::Extrinsic>::SignaturePayload)> {
		// This is the simplest setup we can do
		Some((call, (index, ())))

Getting the Transaction Pool and Off-chain State

When writing test cases for off-chain workers, we need to look into the transaction pool and current off-chain state to ensure a certain transaction has made its way, and was passed with the right parameters and signature. So in addition to the regular test environment TestExternalities, we also need to return references to the transaction pool state and off-chain state for future inspection.

src: pallets/offchain-demo/src/

fn main() {
pub struct ExtBuilder;

impl ExtBuilder {
	pub fn build() -> (TestExternalities, Arc<RwLock<PoolState>>, Arc<RwLock<OffchainState>>) {
		const PHRASE: &str = "expire stage crawl shell boss any story swamp skull yellow bamboo copy";

		// Getting the transaction pool and off-chain state. Return them for future inspection.
		let (offchain, offchain_state) = testing::TestOffchainExt::new();
		let (pool, pool_state) = testing::TestTransactionPoolExt::new();

		// Initialize the keystore with a default key
		let keystore = KeyStore::new();
			Some(&format!("{}/hunter1", PHRASE))

		// Initialize our genesis config
		let storage = system::GenesisConfig::default()

		// Get the TestExternalities, register additional extension we just set up
		let mut t = TestExternalities::from(storage);

		// Return the externalities and two necessary states
		(t, pool_state, offchain_state)

Testing Off-chain Worker

When we write tests for off-chain workers, we should test only what our off-chain workers do. For example, when our off-chain workers will eventually make a signed transaction to dispatch function A, which does B, C, and D, we write our test for the off-chain worker to test only if function A is dispatched. But whether function A actually does B, C, and D should be tested separately in another test case. This way we keep our tests more robust.

This is how we write our test cases.

src: pallets/offchain-demo/src/

fn main() {
fn offchain_send_signed_tx() {
	let (mut t, pool_state, offchain_state) = ExtBuilder::build();

	t.execute_with(|| {
		// when
		let num = 32;
		// then

		// Test only one transaction is in the pool.
		let tx = pool_state.write().transactions.pop().unwrap();

		let tx = TestExtrinsic::decode(&mut &*tx).unwrap();
		// Test the transaction is signed
		assert_eq!(tx.signature.unwrap().0, 0);
		// Test the transaction is calling the expected extrinsics with expected parameters
		assert_eq!(, Call::submit_number_signed(num));

We test that when OffchainDemo::send_signed(num) function is being called,

  • There is only one transaction that made it to the transaction pool.
  • The transaction is signed.
  • The transaction is calling the Call::submit_number_signed on-chain function with the parameter num.

What's performed by the Call::submit_number_signed on-chain function is tested in another test case, which would be similar to how you test for dispatched extrinsic calls.