Needs a headless system on linux to run tests

[andrewdavidmackenzie]

Fixes #444

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 29%. Comparing base (e2ecebe) to head (5565d25). Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #445 +/- ## ===================================== Coverage 29% 29% ===================================== Files 40 40 Lines 4899 4899 ===================================== Hits 1401 1401 Misses 3498 3498 ``` | [Flag](https://app.codecov.io/gh/andrewdavidmackenzie/pigg/pull/445/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andrew+Mackenzie) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/andrewdavidmackenzie/pigg/pull/445/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andrew+Mackenzie) | `29% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andrew+Mackenzie#carryforward-flags-in-the-pull-request-comment) to find out more.

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