Unit Tests: utils and task

[jamesmcclain]

Overview

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Checklist

• Ran scripts/format_code and commited any changes
• Documentation updated if needed
• PR has a name that won't get you publicly shamed for vagueness

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Testing Instructions

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Closes #496
Closes #498
Depends on #490

[codecov]

Codecov Report

Merging #497 into develop will increase coverage by 0.82%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #497      +/-   ##
===========================================
+ Coverage    66.02%   66.84%   +0.82%     
===========================================
  Files          174      155      -19     
  Lines         7331     6895     -436     
===========================================
- Hits          4840     4609     -231     
+ Misses        2491     2286     -205

Impacted Files	Coverage Δ
rastervision/utils/files.py	89.47% <100%> (+18.04%)	⬆️
rastervision/filesystem/local_filesystem.py	97.75% <0%> (-1.13%)	⬇️
rastervision/runner/aws_batch_experiment_runner.py	16.66% <0%> (ø)	⬆️
rastervision/data/raster_source/__init__.py
rastervision/data/label_store/__init__.py
rastervision/utils/filter_geojson.py
rastervision/experiment/__init__.py
rastervision/task/object_detection.py
rastervision/backend/__init__.py
rastervision/__init__.py
... and 13 more

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