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Exercise - Test your smart contract

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In this part, we write a new JavaScript test for our shipping contract. We could instead use Solidity to write the test, but JavaScript is used more commonly. To test our smart contract, we use Truffle.

Begin the testing

Let's begin by creating a new test file.

1. In the Explorer pane, hover over the test folder and right-click. Choose New File and create a new file called TestShipping.js.

2. Copy and paste the following code in the test file:

   const ShippingStatus= artifacts.require("./Shipping.sol");
   contract('Shipping', () => {
   
     it("should return the status Pending", async ()=> {
       // Instance of our deployed contract
       const instance = await ShippingStatus.deployed();
       // Checking the initial status in our contract
       const status = await instance.Status();
       // Checking if the status is initially Pending as set in the constructor
       assert.equal(status, "Pending");
     });
   it("should return the status Shipped", async ()=> {
   // Instance of our deployed contract
       const instance = await ShippingStatus.deployed();
   
       // Calling the Shipped() function
       await instance.Shipped();
   
       // Checking the initial status in our contract
       const status = await instance.Status();
   
       // Checking if the status is Shipped
       assert.equal(status, "Shipped");
     });
   
       it("should return the status Delivered", async ()=> {
   
       // Instance of our deployed contract
       const instance = await ShippingStatus.deployed();
   
       // Calling the Shipped() function
       await instance.Delivered();
   
       // Checking the initial status in our contract
       const status = await instance.Status();
   
       // Checking if the status is Delivered
       assert.equal(status, "Delivered");
     });
   });
   

Event test

We'll use the truffle-assertions package to test the events that are sent in the contract. By using this package, we can assert that our events are emitted during the transaction.

1. In the terminal, install the library by typing npm install truffle-assertions.

2. Add the following code to the test file on line 2, after you require the ShippingStatus contract:

   const truffleAssert = require('truffle-assertions');
   

3. Add a test to confirm that the event returns the expected description. Place this test after the last test in the file. Add it in a new line, right before the last line's set of closing braces.

     it('should return correct event description', async()=>{
   
       // Instance of our deployed contract
       const instance = await ShippingStatus.deployed();
   
       // Calling the Delivered() function
       const delivered = await instance.Delivered();
   
       // Check event description is correct
       truffleAssert.eventEmitted(delivered, 'LogNewAlert', (event) =>{
         return event.description == 'Your package has arrived';
       });
     });
   
   

Using async/await

The function .deployed() returns a promise. So we use await in front of the function, and we use async in front of the test code. This setup means that after the contract is deployed, we won't move forward with our test until the promise is fulfilled.

This pattern is commonly used in tests because almost all smart contract transactions are asynchronous. They're asynchronous because transactions need to be validated or mined before they're added to the blockchain ledger.

Overall, you should aim for 100 percent test coverage for your contract, especially if you plan to deploy to the main Ethereum network, or Main Net.

Run the test

In the terminal, type:

truffle test

You should see that all tests pass successfully:

  Contract: HelloBlockchain
    ✓ testing ResponseMessage of HelloBlockchain
    ✓ testing Responder of HelloBlockchain
    ✓ testing RequestMessage of HelloBlockchain
    ✓ testing State of HelloBlockchain
    ✓ testing Requestor of HelloBlockchain
    ✓ testing SendRequest of HelloBlockchain (51ms)
    ✓ testing SendResponse of HelloBlockchain (46ms)

  Contract: Shipping
    ✓ should return the status Pending
    ✓ should return the status Shipped (59ms)
    ✓ should return the status Delivered (58ms)
    ✓ should return correct event description (39ms)

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