Improve code coverage

[rogerwwww]

No description provided.

[codecov]

Codecov Report

Merging #43 (f1d3e86) into main (ea49cbd) will increase coverage by 1.16%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #43      +/-   ##
==========================================
+ Coverage   87.65%   88.82%   +1.16%     
==========================================
  Files          17       17              
  Lines        6359     6353       -6     
==========================================
+ Hits         5574     5643      +69     
+ Misses        785      710      -75     

Impacted Files	Coverage Δ
pygmtools/tensorflow_backend.py	94.53% <0.00%> (-0.02%)	⬇️
pygmtools/numpy_backend.py	94.63% <0.00%> (+1.22%)	⬆️
pygmtools/pytorch_backend.py	94.36% <0.00%> (+1.56%)	⬆️
pygmtools/jittor_backend.py	93.77% <0.00%> (+1.76%)	⬆️
pygmtools/paddle_backend.py	93.85% <0.00%> (+2.19%)	⬆️
pygmtools/multi_graph_solvers.py	82.85% <0.00%> (+2.85%)	⬆️
pygmtools/utils.py	83.92% <0.00%> (+4.28%)	⬆️

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