I 
the Test Helpers. (I am biased 
).
I upgraded my tests for https://github.com/abcoathup/Simple777Token and got the following error which had me stumped. Similar tests worked on https://github.com/OpenZeppelin/openzeppelin-contracts.
TypeError: this.erc1820.setInterfaceImplementer is not a function
I had forgotten that migrations were run as part of truffle test (even though in my tests I create new contract instances in beforeEach).
As per how to upgrade from 0.4 I needed to change in my migrations (2_deploy.js)
require('@openzeppelin/test-helpers/configure')({ web3 });
to
require('@openzeppelin/test-helpers/configure')({ provider: web3.currentProvider, environment: 'truffle' });