Truffle – Get address(0) in Truffle Test

Yes you can, do your test in Javascript.

In your test you can initialize it like this:

const MyContract = artifacts.require('MyContract');

contract('MyContract', accounts => {
  const owner = accounts[0];
  const alice = accounts[1];
  const bob = accounts[2];

  it('should do something', async () => {
    const contract = await MyContract.deployed();
    await contract.buy(price, data, { from: alice });
    await contract.buy(price, data, { from: bob });
    assert.equal(...);
  });
});

Notice the accounts variable. Hope this helps.

You have two different issues here:

First, the syntax addExam().call(...) is incorrect.

It should be either addExam.call(...) or addExam(...).

Second, the usage of call by itself is incorrect.

Since function addExam changes the state of your contract, you should use sendTransaction.

In short, change this:

instance.addExam().call(hash_test, {from: accounts[0]})

To this:

instance.addExam.sendTransaction(hash_test, {from: accounts[0]})

Or to this:

instance.addExam(hash_test, {from: accounts[0]})