BUG: cannot import file_object_ref from xoscar directly

[ChengjieLi28]

What do these changes do?

Related issue number

Fixes #xxxx

Check code requirements

• [ ] tests added / passed (if needed)
• [ ] Ensure all linting tests pass

[codecov[bot]]

Codecov Report

Merging #39 (8583264) into main (7d2f12f) will decrease coverage by 0.27%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
- Coverage   94.08%   93.82%   -0.27%     
==========================================
  Files          43       43              
  Lines        3399     3399              
  Branches      675      675              
==========================================
- Hits         3198     3189       -9     
- Misses        132      139       +7     
- Partials       69       71       +2     

Flag	Coverage Δ
unittests	93.67% <ø> (-0.24%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
python/xoscar/backends/indigen/pool.py	93.33% <ø> (ø)
python/xoscar/backends/pool.py	95.94% <ø> (ø)

... and 6 files with indirect coverage changes