feat: update the test and doc

[LongxingTan]

Description

This PR ...

Checklist

• Linked issues (if existing)
• Amended changelog.md for large changes (and added myself there as contributor)
• Added/modified tests
• Used pre-commit hooks when committing to ensure that code is compliant with hooks. Install hooks with pre-commit install.
  To run hooks independent of commit, execute pre-commit run --all-files

Thank you for joining. Have fun coding!

[codecov]

Codecov Report

❌ Patch coverage is 63.62297% with 247 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (master@5d50872). Learn more about missing BASE report.
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
tfts/data/get_data.py	9.27%	88 Missing ⚠️
tfts/tasks/pipeline.py	17.97%	73 Missing ⚠️
tfts/models/auto_model.py	30.30%	23 Missing ⚠️
tfts/data/timeseries.py	30.00%	14 Missing ⚠️
tfts/trainer.py	40.90%	13 Missing ⚠️
tfts/losses/loss.py	31.25%	11 Missing ⚠️
tfts/tasks/base.py	43.75%	9 Missing ⚠️
tfts/layers/graph_layer.py	94.39%	6 Missing ⚠️
tfts/layers/dense_layer.py	87.50%	3 Missing ⚠️
tfts/generator.py	71.42%	2 Missing ⚠️
... and 3 more

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #76   +/-   ##
=========================================
  Coverage          ?   81.46%           
=========================================
  Files             ?       55           
  Lines             ?     4807           
  Branches          ?        0           
=========================================
  Hits              ?     3916           
  Misses            ?      891           
  Partials          ?        0           

Flag	Coverage Δ
cpu	81.46% <63.62%> (?)
unittest	81.46% <63.62%> (?)

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