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Part 2: Inter-contract calls and testing

Previously, you learned how to create your first dApp. In this second session, you will enhance your skills on:

  • How to do inter-contract calls.
  • How to use views.
  • How to do unit & mutation tests.

On the first version of the poke game, you were able to poke any deployed contract. Now, you will add a new function to store on the trace an additional feedback message coming from another contract.

Poke and Get Feedback sequence diagram

Get the code

Get the code from the first session:

git clone

Reuse the code from the previous smart contract:

Install all libraries locally:

cd solution && npm i && cd app && yarn install && cd ..

Modify the poke function

Change the storage to reflect the changes:

  • If you poke directly, you just register the contract's owner address and no feedback.
  • If you poke and ask to get feedback from another contract, then you register the other contract address and an additional feedback message.

Here the new sequence diagram of the poke function.

  1. Edit ./contracts/pokeGame.jsligo and replace storage definition by this one:

    export type pokeMessage = {
    receiver : address,
    feedback : string

    export type storage = {
    pokeTraces : map<address, pokeMessage>,
    feedback : string
  2. Replace your poke function with theses lines:

    const poke = (_ : unit, store : storage) : return_ => {
    let feedbackMessage = {receiver : Tezos.get_self_address() ,feedback: ""};
    return [ list([]) as list<operation>, {,
    pokeTraces : Map.add(Tezos.get_source(), feedbackMessage, store.pokeTraces) }];


    • do a copy by value of your object. Have a look on the Functional updates documentation. Note: you cannot do assignment like this store.pokeTraces=... in JsLIGO, there are no concept of Classes, use Functional updates instead.
    • Map.add(...: Add a key, value entry to a map. For more information about Map.
    • export type storage = {...}; a Record type is declared, it is an object structure.
    • Tezos.get_self_address() is a native function that returns the current contract address running this code. Have a look on Tezos native functions.
    • feedback: "": poking directly does not store feedbacks.
  3. Edit pokeGame.storageList.jsligo to change the storage initialization.

    #import "pokeGame.jsligo" "Contract"

    const default_storage: = {
    pokeTraces: Map.empty as map<address, Contract.pokeMessage>,
    feedback: "kiss"
  4. Compile your contract.

    TAQ_LIGO_IMAGE=ligolang/ligo:1.1.0 taq compile pokeGame.jsligo

    Write a second function pokeAndGetFeedback involving the call to another contract a bit later, let's do unit testing first!

Write unit tests

  1. Add a new unit test smart-contract file unit_pokeGame.jsligo.

    taq create contract unit_pokeGame.jsligo

    ℹ️ Testing documentation can be found here ℹ️ Test module with specific functions here

  2. Edit the file.

    #import "./pokeGame.jsligo" "PokeGame"

    export type main_fn = module_contract<parameter_of PokeGame,>;

    // reset state

    const _ = Test.reset_state(2 as nat, list([]) as list<tez>);

    const faucet = Test.nth_bootstrap_account(0);

    const sender1: address = Test.nth_bootstrap_account(1);

    const _2 = Test.log("Sender 1 has balance : ");

    const _3 = Test.log(Test.get_balance_of_address(sender1));

    const _4 = Test.set_baker(faucet);

    const _5 = Test.set_source(faucet);

    export const initial_storage = {
    pokeTraces: Map.empty as map<address, PokeGame.pokeMessage>,
    feedback: "kiss"

    export const initial_tez = 0mutez;


    export const _testPoke = (
    taddr: typed_address<parameter_of PokeGame,>,
    s: address
    ): unit => {
    const contr = Test.to_contract(taddr);
    const contrAddress = Tezos.address(contr);
    Test.log("contract deployed with values : ");
    const status = Test.transfer_to_contract(contr, Poke(), 0 as tez);
    const store: = Test.get_storage(taddr);
    //check poke is registered

    match(Map.find_opt(s, store.pokeTraces)) {
    when (Some(pokeMessage)):
    do {
    assert_with_error( == "",
    "feedback " + + " is not equal to expected "
    + "(empty)"
    pokeMessage.receiver == contrAddress,
    "receiver is not equal"
    when (None()):
    assert_with_error(false, "don't find traces")

    // TESTS //

    const testSender1Poke =
    (): unit => {
    const orig =
    Test.originate(contract_of(PokeGame), initial_storage, initial_tez);
    _testPoke(orig.addr, sender1);


    • #import "./pokeGame.jsligo" "PokeGame" to import the source file as module in order to call functions and use object definitions.
    • export type main_fn it will be useful later for the mutation tests to point to the main function to call/mutate.
    • Test.reset_state ( 2... this creates two user accounts on the test environment.
    • Test.nth_bootstrap_account this return the nth account from the environment.
    • Test.to_contract(taddr) and Tezos.address(contr) are util functions to convert typed addresses, contract and contract addresses.
    • let _testPoke = (s : address) : unit => {...} declaring function starting with _ is escaping the test for execution. Use this to factorize tests changing only the parameters of the function for different scenarios.
    • Test.set_source do not forget to set this value for the transaction signer.
    • Test.transfer_to_contract(CONTRACT, PARAMS, TEZ_COST) A transaction to send, it returns an operation.
    • Test.get_storage this is how to retrieve the contract's storage.
    • assert_with_error(CONDITION,MESSAGE) Use assertion for unit testing.
    • const testSender1Poke = ... This test function will be part of the execution report.
    • Test.originate_module(MODULE_CONVERTED_TO_CONTRACT,INIT_STORAGE, INIT_BALANCE) It originates a smart contract into the Test environment. A module is converted to a smart contract.
  3. Run the test.

    TAQ_LIGO_IMAGE=ligolang/ligo:1.1.0 taq test unit_pokeGame.jsligo

    Output should give you intermediary logs and finally the test results.

    │ Contract │ Test Results │
    │ unit_pokeGame.jsligo │ "Sender 1 has balance : " │
    │ │ 3800000000000mutez │
    │ │ "contract deployed with values : " │
    │ │ KT1KwMWUjU6jYyLCTWpZAtT634Vai7paUnRN(None) │
    │ │ Success (2130n) │
    │ │ {feedback = "kiss" ; pokeTraces = [tz1TDZG4vFoA2xutZMYauUnS4HVucnAGQSpZ -> {feedback = "" ; receiver = KT1KwMWUjU6jYyLCTWpZAtT634Vai7paUnRN}]} │
    │ │ Everything at the top-level was executed. │
    │ │ - testSender1Poke exited with value (). │
    │ │ │
    │ │ 🎉 All tests passed 🎉 │

Do an inter contract call

To keep things simple, 2 versions of the same smart contract are deployed to simulate inter-contract call and get the feedback message (cf. sequence diagram).

Create a new poke function PokeAndGetFeedback: (other : address) with a second part function PokeAndGetFeedbackCallback: (feedback : returned_feedback) as a callback. Calling a contract is asynchronous, this is the reason it is done in two times.

The function to call on the second contract is GetFeedback: (contract_callback: oracle_param) and returns a feedback message.

Very often, this kind of contract is named an Oracle, because generally its storage is updated by an offchain scheduler and it exposes data to any onchain smart contracts.

  1. Edit the file pokeGame.jsligo, to define new types:

    type returned_feedback = [address, string]; //address that gives feedback and a string message

    type oracle_param = contract<returned_feedback>;

    Explanations :

    • type returned_feedback = [address, string] the parameters of an oracle function always start with the address of the contract caller and followed by the return objects.
    • type oracle_param = contract<returned_feedback> the oracle parameters need to be wrapped inside a typed contract.
  2. Write the missing functions, starting with getFeedback. Add this new function at the end of the file.

    const getFeedback = (contract_callback : contract<returned_feedback>, store : storage): return_ => {
    let op : operation = Tezos.transaction(
    (0 as mutez),
    return [list([op]) ,store];
    • Tezos.transaction(RETURNED_PARAMS,TEZ_COST,CALLBACK_CONTRACT) the oracle function requires to return the value back to the contract caller that is passed already as first parameter.
    • return [list([op]) ,store] this time, you return a list of operations to execute, there is no need to update the contract storage (but it is a mandatory return object).
  3. Add now, the first part of the function pokeAndGetFeedback.

    const pokeAndGetFeedback = (oracleAddress: address, store: storage): return_ => {
    //Prepares call to oracle

    let call_to_oracle = (): contract<oracle_param> => {
    return match(
    Tezos.get_entrypoint_opt("%getFeedback", oracleAddress) as
    ) {
    when (None()):
    when (Some(contract)):
    // Builds transaction

    let op: operation =
    Tezos.self("%pokeAndGetFeedbackCallback") as
    (0 as mutez),
    return [list([op]), store];
    • Tezos.get_entrypoint_opt("%getFeedback",oracleAddress) you require to get the oracle contract address. Then you want to call a specific entrypoint of this contract. The function name is always starting with % with always the first letter in lowercase (even if the code is different).
    • Tezos.transaction(((Tezos.self("%pokeAndGetFeedbackCallback") as contract<returned_feedback>)),TEZ_COST,call_to_oracle()) The transaction takes as first param the entrypoint of for the callback that the oracle uses to answer the feedback, the tez cost and the oracle contract you got just above as transaction destination.
  4. Write the last missing function pokeAndGetFeedbackCallback, receive the feedback and finally store it.

    const pokeAndGetFeedbackCallback = (feedback : returned_feedback, store : storage) : return_ => {
    let feedbackMessage = {receiver : feedback[0] ,feedback: feedback[1]};
    return [ list([]) as list<operation>, {,
    pokeTraces : Map.add(Tezos.get_source(), feedbackMessage , store.pokeTraces) }];
    • let feedbackMessage = {receiver : feedback[0] ,feedback: feedback[1]} prepares the trace including the feedback message and the feedback contract creator.
    • {,pokeTraces : Map.add(Tezos.get_source(), feedbackMessage , store.pokeTraces) } add the new trace to the global trace map.
  5. Compile the contract.

    Note: Remove the file pokeGame.parameterList.jsligo to remove all unnecessary error logs as there is need to maintain this file anymore.

    TAQ_LIGO_IMAGE=ligolang/ligo:1.1.0 taq compile pokeGame.jsligo
  6. (Optional) Write a unit test for this new function pokeAndGetFeedback.

Use views instead of inter-contract call

As you saw on the previous step, inter-contract calls makes the business logic more complex but not only, thinking about the cost is even worst.

In this training, the oracle is providing a read-only storage that can be replaced by a view instead of a complex and costly callback.

See documentation here about onchain views.

⚠️ Comment below functions (with /* */ syntax or // syntax) or just remove it, it is no more useful ⚠️

  • pokeAndGetFeedbackCallback
  • getFeedback
  1. Edit function pokeAndGetFeedback to call view instead of a transaction.

    const pokeAndGetFeedback = (oracleAddress: address, store: storage): return_ => {
    //Read the feedback view

    let feedbackOpt: option<string> =
    Tezos.call_view("feedback", unit, oracleAddress);
    match(feedbackOpt) {
    when (Some(feedback)):
    do {
    let feedbackMessage = { receiver: oracleAddress, feedback: feedback };
    return [
    list([]) as list<operation>,
    pokeTraces: Map.add(
    when (None()):
    failwith("Cannot find view feedback on given oracle address")
  2. Declare the view at the end of the file. Do not forget the annotation @view !

    export const feedback = (_: unit, store: storage): string => { return };
  3. Compile the contract.

    TAQ_LIGO_IMAGE=ligolang/ligo:1.1.0 taq compile pokeGame.jsligo
  4. (Optional) Write a unit test for the updated function pokeAndGetFeedback.

Write mutation tests

LIGO provides mutations testing through the Test library. Mutation tests are like testing your tests to see if your unit tests coverage is strong enough. Bugs, or mutants, are automatically inserted into your code. Your tests are run on each mutant.

If your tests fail then the mutant is killed. If your tests passed, the mutant survived. The higher the percentage of mutants killed, the more effective your tests are.

Example of mutation features for other languages

  1. Create a file mutation_pokeGame.jsligo.

    taq create contract mutation_pokeGame.jsligo
  2. Edit the file.

    #import "./pokeGame.jsligo" "PokeGame"

    #import "./unit_pokeGame.jsligo" "PokeGameTest"

    // reset state

    const _ = Test.reset_state(2 as nat, list([]) as list<tez>);

    const faucet = Test.nth_bootstrap_account(0);

    const sender1: address = Test.nth_bootstrap_account(1);

    const _1 = Test.log("Sender 1 has balance : ");

    const _2 = Test.log(Test.get_balance_of_address(sender1));

    const _3 = Test.set_baker(faucet);

    const _4 = Test.set_source(faucet);

    const _tests = (
    ta: typed_address<parameter_of PokeGame,>,
    _: michelson_contract<parameter_of PokeGame,>,
    _2: int
    ): unit => { return PokeGameTest._testPoke(ta, sender1); };

    const test_mutation =
    (): unit => {
    const mutationErrorList =
    match(mutationErrorList) {
    when ([]):
    when ([head, ..._tail]):
    do {
    Test.assert_with_error(false, Test.to_string(head[1]))


    • #import <SRC_FILE> <NAMESPACE>: import your source code that will be mutated and your unit tests. For more information module doc.
    • const _tests = (ta: typed_address<parameter_of PokeGame,>, _: michelson_contract, _: int) : unit => {...: you need to provide the test suite that will be run by the framework. Just point to the unit test you want to run.
    • const test_mutation = (() : unit => {: this is the definition of the mutations tests.
    • Test.originate_module_and_mutate_all(CONTRACT_TO_MUTATE, INIT_STORAGE, INIT_TEZ_COST, UNIT_TEST_TO_RUN): This will take the first argument as the source code to mutate and the last argument as unit test suite function to run over. It returns a list of mutations that succeed (if size > 0 then bad test coverage) or empty list (good, even mutants did not harm your code).
  3. Run the test.

    TAQ_LIGO_IMAGE=ligolang/ligo:1.1.0 taq test mutation_pokeGame.jsligo


    === Error messages for mutation_pokeGame.jsligo ===
    File "contracts/mutation_pokeGame.jsligo", line 43, characters 12-66:
    42 | Test.log(head);
    43 | Test.assert_with_error(false, Test.to_string(head[1]))
    44 | }

    Test failed with "Mutation at: File "contracts/pokeGame.jsligo", line 52, characters 15-66:
    51 | when (None()):
    52 | failwith("Cannot find view feedback on given oracle address")
    53 | };

    Replacing by: "Cannot find view feedback on given oracle addressCannot find view feedback on given oracle address".
    File "contracts/mutation_pokeGame.jsligo", line 43, characters 12-66 ,
    File "contracts/mutation_pokeGame.jsligo", line 43, characters 12-66 ,
    File "contracts/mutation_pokeGame.jsligo", line 28, character 2 to line 47, character 5

    │ Contract │ Test Results │
    │ mutation_pokeGame.jsligo │ Some tests failed :( │

    Invaders are here.

    What happened ?

    The mutation has altered a part of the code which is not tested, it was not covered, so the unit test passed.

    For a short fix, tell the Library to ignore this function for mutants.

  4. Go to your source file pokeGame.jsligo, and annotate the function pokeAndGetFeedback with @no_mutation.

    const pokeAndGetFeedback ...
  5. Run again the mutation tests.

    TAQ_LIGO_IMAGE=ligolang/ligo:1.1.0 taq test mutation_pokeGame.jsligo


    │ Contract │ Test Results │
    │ mutation_pokeGame.jsligo │ "Sender 1 has balance : " │
    │ │ 3800000000000mutez │
    │ │ "contract deployed with values : " │
    │ │ KT1L8mCbuTJXKq3CDoHDxqfH5aj5sEgAdx9C(None) │
    │ │ Success (1330n) │
    │ │ {feedback = "kiss" ; pokeTraces = [tz1hkMbkLPkvhxyqsQoBoLPqb1mruSzZx3zy -> {feedback = "" ; receiver = KT1L8mCbuTJXKq3CDoHDxqfH5aj5sEgAdx9C}]} │
    │ │ "Sender 1 has balance : " │
    │ │ 3800000000000mutez │
    │ │ Everything at the top-level was executed. │
    │ │ - test_mutation exited with value (). │
    │ │ │
    │ │ 🎉 All tests passed 🎉 │

Update the frontend

  1. Reuse the dApp files from previous session.

  2. Redeploy a new version of the smart contract.

    Note: You can set feedback value to any action other than default kiss string (it is more fun for other to discover it).

    TAQ_LIGO_IMAGE=ligolang/ligo:1.1.0 taq compile pokeGame.jsligo
    taq generate types ./app/src
    taq deploy -e "testing"
  3. Adapt the frontend application code. Edit App.tsx, and add new import.

    import { address } from './type-aliases';
  4. Add new React variable after userBalance definition.

    const [contractToPoke, setContractToPoke] = useState<string>('');
  5. Change the poke function to set entrypoint to pokeAndGetFeedback.

    const poke = async (
    e: React.FormEvent<HTMLFormElement>,
    contract: api.Contract
    ) => {
    let c: PokeGameWalletType = await'' + contract.address);
    try {
    const op = await c.methods
    .pokeAndGetFeedback(contractToPoke as address)
    await op.confirmation();
    alert('Tx done');
    } catch (error: any) {
    console.table(`Error: ${JSON.stringify(error, null, 2)}`);
  6. Change the display to a table changing by:

    <table><thead><tr><th>address</th><th>trace "contract - feedback - user"</th><th>action</th></tr></thead><tbody>
    { => <tr><td style={{borderStyle: "dotted"}}>{contract.address}</td><td style={{borderStyle: "dotted"}}>{( !== null && !== null && Object.entries( > 0)?Object.keys( : string)=>[k].receiver+" "[k].feedback+" "+k+", "):""}</td><td style={{borderStyle: "dotted"}}><form onSubmit={(e) =>poke(e,contract)}><input type="text" onChange={e=>setContractToPoke(e.currentTarget.value)} placeholder='enter contract address here' /><button type='submit'>Poke</button></form></td></tr>)}
  7. Relaunch the app.

    cd app
    yarn install
    yarn dev

    On the listed contract, choose your line and input the address of the contract you will receive a feedback. Click on poke.

    The dApp page showing the result of the poke action.

    This time, the logged user will receive a feedback from a targeted contract (as input of the form) via any listed contract (the first column of the table).

  8. Refresh manually clicking on Fetch contracts button.

    Poke other developer's contract to discover their contract hidden feedback when you poke them.


Now, you are able to call other contracts, use views and test you smart contract before deploying it.

On next training, you will learn how to use tickets.

When you are ready, continue to Part 3: Tickets.