embark-dtwitter-workshop/instructions/5 Coding: tests.md

Contract tests

Now that we have our contract written, we can use the code generation provided by EmbarkJS to write our contract unit test cases for test-driven development. Embark will code generate a DTwitter javascript object for us from our contract and make it accessible in our dApp by way of the DTwitter object.

Additionally, EmbarkJS allows us to interact with decentralised storage (IPFS and Swarm) and decentralised communication (Whisper), which are all configurable in config files.

Create account transaction should be successful

Our first test is to ensure that our createAccount transaction is sent successfully. Let's fill in the code that calls our createAccount contract function:

// do the create account tx
const createAccountTx = await DTwitter.methods.createAccount(username, description).send();

Notice the .send() at the end. This is required when we are sending a transaction that will modify the state of contract. In this case, we are modifying the state by adding a user to the users mapping.

Should create user

After our successful createAccount transaction, this should have created a user. In our test, let's fill in the code to retrieve a user from the contract.

// Get user details from contract
const user = await DTwitter.methods.users(web3.utils.keccak256(username)).call();

This time we used a .call(). Why? Because in this case we are not modifying the state of the contract, and simplying querying data from it. Changing state costs gas, so we use .send(), while querying state is free, so we use .call().

Should create owner for default account

The createAccount function should have also created an entry in the owners mapping with our defaultAccount, which we check in the next test. This is how we retrieve an owner from the owners mapping:

// read from the owners mapping the value associated with the defaultAccount
const usernameHash = await DTwitter.methods.owners(web3.eth.defaultAccount).call();

User exists should be true

We can use our userExists function in the contract to check if a usernameHash exists. This will later be used for username validation in the dApp. Our test for userExists can be completed using:

// Check the usernamehash exists
const exists = await DTwitter.methods.userExists(usernameHash).call();

Edit Account should update user details

After a call to editAccount, our user's details should be updated. This unit test can be completed by adding the following:

1. Call edit account

   await DTwitter.methods.editAccount(usernameHash, updatedDescription, updatedImageHash).send();
   

2. Then fetch the user details with the usernamehash

   const updatedUserDetails = await DTwitter.methods.users(usernameHash).call();
   

Tweet event should fire when there is a tweet

We need to ensure that our contract events subscription works correctly when someone creates a new tweet via the tweet function. In our unit test, we can add the following:

1. Subscribe to the NewTweet event

   DTwitter.events.NewTweet({
       filter: { _from: usernameHash },
       fromBlock: 0
   })
   .on('data', (event) => {
       assert.equal(event.returnValues.tweet, tweetContent);
   });
   

2. Do the tweet

   await DTwitter.methods.tweet(tweetContent).send();
   

Run tests

Let's run the tests to ensure they are all passing. Type quit in the Embark consle, then run:

run_embark test

Test results

Your test results should appear similar to the following:

DTwitter contract
    ✓ transaction to create a dtwitter user 'testhandle' with description 'test description' should be successful (114ms)
    ✓ should have created a user 'testhandle' (60ms)
    ✓ should have created an owner for our defaultAccount
    ✓ should know 'testhandle' exists (49ms)
    ✓ should be able to edit 'testhandle' user details (186ms)
    ✓ should be able to add a tweet as 'testhandle' and receive it via contract event (54ms)

Note: there is a known error with ganache that sometimes causes last test does to fail with the error ERROR: The returned value is not a convertible string. We are currently investigating this issue.