Use this in tests

[nventuro]

Some tests still have global(ish) state, we should move towards storing those in this.

Part of #1091.

[Aniket-Engg]

@nventuro I think most of the tests are following this. Can you please point to the files lacking this?

[nventuro]

To clarify, this doesn't refer to configuration variables (e.g. const cap = ether(20);), but to things like

let token;
beforeEach(async function () {
  token = await Token.new();
});

examples/SimpleToken is guilty of this, as is MerkleProof, DetailedERC20, and ReentracnyGuard. There may be more examples of this, but I'm not sure.

[Aniket-Engg]

I checked each test file. Changes were required only in the files mentioned by @nventuro . Still if anyone finds that I missed something, Please add here.