[ISSUE-190] Added test stub to endOf manipulator function

[jama5262]

What does this PR do?

Added test stub to endOf manipulator function

Resolve #190

[codecov[bot]]

Codecov Report

Base: 96.17% // Head: 96.24% // Increases project coverage by +0.06% :tada:

Coverage data is based on head (7630a51) compared to base (9aa7ca9). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #191 +/- ## =========================================== + Coverage 96.17% 96.24% +0.06% =========================================== Files 34 34 Lines 1515 1516 +1 =========================================== + Hits 1457 1459 +2 + Misses 58 57 -1 ``` | [Impacted Files](https://codecov.io/gh/jama5262/jiffy/pull/191?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed) | Coverage Δ | | |---|---|---| | [lib/src/manipulator.dart](https://codecov.io/gh/jama5262/jiffy/pull/191?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed#diff-bGliL3NyYy9tYW5pcHVsYXRvci5kYXJ0) | `100.00% <100.00%> (+0.72%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed)

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