First Test for the Mock Sequence

[upstarter]

Create simple behavioral test for the MockSeq1. Test that it runs all of it's children, one after the other in time, where no successor runs before a predecessor (since we aim to be fully async).

We can either use espec or the elixir builtin testing library. We can setup the TestMockSeq1 to have more children (simple actions would be best) for now until we get factories or fixtures.