How does "beforeEach" work / question on unit testing in lesson 7 (~11 hours 24 minutes in)

[tmcdonough]

If I am going to run a test, such as (some pseudo-code for readability):

describe("FundMe", function() {
    beforeEach(async function() {
        await deployments.fixture(["all"]) // deploy all scripts with "all" tag
        fundMe = await getContract("FundMe", deployer) // most recently deployed fundme contract, which we just deployed.
    })
    describe("fund", function() {
        it("Updates the amount funded data structure", async function() {
            await fundMe.fund({ value: sendValue })
            const response = await fundMe.addressToAmountFunded(deployer)
            assert.equal(response.toString(), sendValue.toString())
        })
        it("Adds funder to array of funders", async function() {
            await fundMe.fund({ value: sendValue })
            const funder = await fundMe.funders(1) // NOTE: I changed this from PC's code from 1 to 0 for this discussion.
            assert.equal(funder, deployer)
        })        
    })

Testing both "it" statements within the "fund" describe function will revert on test #2. I had assumed either 1 or 0 for the funders index would work, since - I thought - this would be the second fundMe.fund() call to the most recently deployed fundMe contract. Since it reverts, does this suggest the "beforeEach" is called before each "it" function (not just before each describe)?

More succinctly:

How many times is fundMe deployed in the above test? Does "beforeEach" run before each subsequent "describe" or before each subsequent "describe->it"?

[alymurtazamemon]

@tmcdonough No, you are confusing here, each function runs a new copy you can say until you do not have beforeEach.

Here you have only 1 beforeEach that deploys and gets the instance of the FundMe contract, after that it behaves that there is no account 0 amount funded to contract.

Your first test is correct but for the second you need to compare it with funders(0).

[tmcdonough]

Thanks @alymurtazamemon . If there's only one fundMe contract deployed, wouldn't both index 0 and index 1 in the funders array be set to the same address? Since that address calls "fund" in the two it() tests? That's why I had assumed 1 should work, as well.

[alymurtazamemon]

@tmcdonough No no it does not work like that. You can think of it as a fresh copy every time except it runs the code of BeforeEach for all it functions.

[tmcdonough]

@alymurtazamemon Got it, thanks.

So, just to be 100% clear. My initial question asked: How many times is fundMe deployed in the above test? Does "beforeEach" run before each subsequent "describe" or before each subsequent "describe->it"?

The answer is: "It is deployed before each subsequent 'it'", correct?

[alymurtazamemon]

@tmcdonough Sorry not getting what you are trying to say. But let me clarify.

Only here the FundMe will deploy only once.

beforeEach(async function() {
    await deployments.fixture(["all"]) // deploy all scripts with "all" tag
    fundMe = await getContract("FundMe", deployer) // most recently deployed fundme contract, which we just deployed.
})

After that, it will be available for all child describe and it functions.

[krakxn]

A brief snapshot for beforeEach

describe('hooks', function () {
  before(function () {
    // runs once before the first test in this block
  });

  after(function () {
    // runs once after the last test in this block
  });

  beforeEach(function () {
    // runs before each test in this block
  });

  afterEach(function () {
    // runs after each test in this block
  });

  // test cases
});

[pacelliv]

@krakxn,

describe("hooks", function () {
    beforeEach(function () {
});

    it("firstTest", function () {
    });

    it("secondTest", function () {
    });

})

If I run yarn hardhat test, this is what I think would happen:

1. The beforeEach() will be executed before the test with the hook "firstTest".
2. The test with the hook firstTest is executed.
3. The beforeEach() is excuted again before the test with the hook "secondTest".
4. The test with the hook secondTest is executed.
5. End of the test.

Can you confirm if my logic is correct?

[krakxn]

Correct.