dreddit-dapp/instructions/5 Coding: Unit Testing.md

Unit testing

Now that we finished coding our contract, we can proceed to build unit testing for it. Embark generates javascript code for interacting with the contract DReddit and will make it possible to use it from both our unit tests and our dApp. There are some tests already implemented in ./test/contract_spec.js, but we will add a couple that illustrate the most common test case scenarios

We should be able to create a post and receive it via contract event

    let receipt = await DReddit.methods.create(web3.utils.fromAscii(ipfsHash)).send();
    const event = receipt.events.NewPost;
    postId = event.returnValues.postId;
    assert.equal(web3.utils.toAscii(event.returnValues.description), ipfsHash);

This test demonstrates how to send a transaction to a contract. Since create() emits an event, we're able to access it in the transaction receipt, and we can use it to perform any assertion we need.

The post should have correct data

    const post = await DReddit.methods.posts(postId).call();
    assert.equal(web3.utils.toAscii(post.description), ipfsHash);
    assert.equal(post.owner, accounts[0]);

On this test, we read data from the chain, without generating a transaction. Notice we use call() instead of send() when invoking the post() function. A call will read the current state of our contract

We should't be able to vote twice for the same post

    try {
      const receipt = await DReddit.methods.vote(postId, 1).send();
      assert.fail('should have reverted before');
    } catch (error){
        assert(error.message.search('revert') > -1, 'Revert should happen');
    }

On this test we can see the pattern to evaluate a transaction that will revert. It involves using a try/catch block, and assert.fail() should be used to guarantee that it will fail the test if it reaches that line. Since vote() will revert, it throws an exception that we capture, and evaluate the error message to determine if the transaction reverted.

Running the tests

To execute the tests and see their result, on a terminal session run:

embark test

Results

The results of your test unit should be similar to the following:

  DReddit contract
    ✓ should be able to create a post and receive it via contract event
    ✓ should return 1 post
    ✓ post should have correct data
    ✓ should not be able to vote in an unexisting post report
    ✓ should be able to vote in a post if account hasn't voted before
    ✓ should be able to vote in a post
    ✓ should't be able to vote twice

  7 passing (163ms)


 > All tests passed