[Refactor] Use post_process function to handle pred result processing.

[mzr1996]

Motivation

In most heads, we need to do some post-processing after getting the pred result. However, downstream tasks, like deploy, may want to override this post-processing function.

Modification

Convert the post-processing in the simple_test function to a standalone method. And all child classes can reuse the method.

BC-breaking (Optional)

No.

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit tests to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects, like MMDet or MMSeg.
• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Merging #390 (fe1441b) into master (df5cec3) will increase coverage by 0.05%.
The diff coverage is 62.50%.

@@            Coverage Diff             @@
##           master     #390      +/-   ##
==========================================
+ Coverage   76.51%   76.56%   +0.05%     
==========================================
  Files          97       97              
  Lines        5224     5206      -18     
  Branches      856      852       -4     
==========================================
- Hits         3997     3986      -11     
+ Misses       1108     1101       -7     
  Partials      119      119              

Flag	Coverage Δ
unittests	76.56% <62.50%> (+0.05%)	⬆️

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

Impacted Files	Coverage Δ
mmcls/models/heads/multi_label_linear_head.py	70.83% <0.00%> (+7.50%)	⬆️
mmcls/models/heads/cls_head.py	81.81% <50.00%> (+10.38%)	⬆️
mmcls/models/heads/multi_label_head.py	64.70% <50.00%> (-0.92%)	⬇️
mmcls/models/heads/linear_head.py	82.60% <100.00%> (-3.60%)	⬇️
mmcls/models/heads/stacked_head.py	96.92% <100.00%> (-0.18%)	⬇️
mmcls/models/heads/vision_transformer_head.py	91.89% <100.00%> (-1.14%)	⬇️

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[grimoire]

Did ClsHead and MultiLabelClsHead share same post_process?
Can we put it in BaseHead?

[mzr1996]

Did ClsHead and MultiLabelClsHead share same post_process?
Can we put it in BaseHead?

Yes, share the same post_process.
Considering BaseHead is an abstract class, I don't confirm if putting post_process in BaseHead is a good practice. It even doesn't have the simple_test method.

[grimoire]

Sure, LGTM!

[Ezra-Yu]

LGTM