Added TimeFrame with passed tests

[startgeek]

Supercedes #1592

[nventuro]

What is we had some sort of 'constructor' to create epochs, which performed these validations? We may also want to force a lower bound on the length (e.g. 30 seconds), to prevent the timestamp manipulation issues already described.

[startgeek]

OK this one you completely lost me can you explain more

[startgeek]

please explain this one

[nventuro]

Sorry, I didn't see all of the comments on the previous pass!
I meant something like this:

function new(uint256 start, uint256 end) internal pure returns (Epoch) {
  require(end >= start + 60); // prevents narrow time frames
  return Epoch(start, end);
}

I'm not sure if Solidity provides a way to disable the 'default constructor' for a struct library (probably not), perhaps we can suggest this feature?

[frangio]

Seems in line with the opaque structs feature we've been dreaming of.

[nventuro]

I'd personally prefer it if these tests were written in a way that they reflected how the return value of TimeFrame functions changes as time passes (e.g. using time.increaseTo), something like:

context before start
  it returns false

  context after start
    beforeEach
      time.advanceToStart

    it returns true

But that's just an idea, I won't block this PR on that :)

[startgeek]

I love this idea but I have a suggestion on top of that
how about I add another test and this test remains as basic functionalities and second test we call it something like advanceTimeFrame or TimeFrameInAction and there I write 9 test's
1.before start
2.very close to starting (1 millisecond before the start)
3.equal to start
4. A little bit after the start (1 millisecond after the start)
5. middle of the time frame
6.very close to the end (1 millisecond before the end)
7.equal to end
8. A little bit after the end (1 millisecond after the end)
9. after the end

let me know your thought's on that

[nventuro]

Those seem great (maybe 1 millisecond is a bit overkill 😅), but why would you also keep the basic tests? You'd be testing the exact same functionality on both.

[startgeek]

whatever you want boss . I make it happen ASAP

[nventuro]

Awesome @catageek, thanks a lot! I left a couple more minor comments.

[nventuro]

Those seem great (maybe 1 millisecond is a bit overkill 😅), but why would you also keep the basic tests? You'd be testing the exact same functionality on both.