Add unit test, some formatting

[codecov-commenter]

Codecov Report

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

Comparison is base (10bd353) 97.88% compared to head (d77d8ea) 97.93%.

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #56 +/- ## ========================================== + Coverage 97.88% 97.93% +0.05% ========================================== Files 5 5 Lines 236 242 +6 ========================================== + Hits 231 237 +6 Misses 5 5 ``` | [Files](https://app.codecov.io/gh/mayer79/missRanger/pull/56?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Michael+Mayer) | Coverage Δ | | |---|---|---| | [R/missRanger.R](https://app.codecov.io/gh/mayer79/missRanger/pull/56?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Michael+Mayer#diff-Ui9taXNzUmFuZ2VyLlI=) | `97.70% <100.00%> (+0.06%)` | :arrow_up: | | [R/pmm.R](https://app.codecov.io/gh/mayer79/missRanger/pull/56?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Michael+Mayer#diff-Ui9wbW0uUg==) | `96.42% <100.00%> (+0.13%)` | :arrow_up: |

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.