Improve test coverage

[odow]

Progress for #32

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@263476a). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #41   +/-   ##
=========================================
  Coverage          ?   88.52%           
=========================================
  Files             ?       17           
  Lines             ?      845           
  Branches          ?        0           
=========================================
  Hits              ?      748           
  Misses            ?       97           
  Partials          ?        0

Impacted Files	Coverage Δ
src/simulate.jl	96.87% <ø> (ø)

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