[Fix] Fix bug of lr updater hook

[zhouzaida]

Fix bug of #887

[Next PR]
I will do more unittest in https://github.com/open-mmlab/mmcv/blob/master/tests/test_runner/test_hooks.py.
But, maybe we should refactor the code test_hooks.py to make the test logic clearer.

├── test_basemodule.py
├── test_checkpoint.py
├── test_dist_utils.py
├── test_fp16.py
├── test_hooks.py
├── test_optimizer.py
├── test_runner.py
└── test_utils.py

to

├── test_basemodule.py
├── test_checkpoint.py
├── test_dist_utils.py
├── test_fp16.py
├── test_hooks
│   ├── test_checkpoint_hook.py
│   └── test_lr_updater_hook.py
├── test_hooks.py
├── test_optimizer.py
├── test_runner.py
└── test_utils.py

[codecov]

Codecov Report

Merging #907 (0ff368e) into master (f0c43fd) will increase coverage by 0.72%.
The diff coverage is 37.31%.

❗ Current head 0ff368e differs from pull request most recent head da386ce. Consider uploading reports for the commit da386ce to get more accurate results

@@            Coverage Diff             @@
##           master     #907      +/-   ##
==========================================
+ Coverage   64.62%   65.34%   +0.72%     
==========================================
  Files         148      148              
  Lines        9354     9390      +36     
  Branches     1698     1715      +17     
==========================================
+ Hits         6045     6136      +91     
+ Misses       2962     2914      -48     
+ Partials      347      340       -7     

Flag	Coverage Δ
unittests	65.34% <37.31%> (+0.72%)	⬆️

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

Impacted Files	Coverage Δ
mmcv/runner/hooks/lr_updater.py	64.38% <0.00%> (+6.83%)	⬆️
mmcv/runner/hooks/momentum_updater.py	60.60% <49.01%> (+9.12%)	⬆️
mmcv/runner/checkpoint.py	69.42% <0.00%> (+1.27%)	⬆️
mmcv/runner/base_runner.py	72.17% <0.00%> (+4.34%)	⬆️
mmcv/runner/hooks/logger/base.py	68.93% <0.00%> (+5.82%)	⬆️
mmcv/runner/hooks/logger/text.py	72.63% <0.00%> (+11.57%)	⬆️

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[hellock]

ping @nbei

[nbei]

Could this pr contain the unit test for the modified parts?

[zhouzaida]

Could this pr contain the unit test for the modified parts?

OK

ping @nbei

[ZwwWayne]

Agree to refactor the test_hooks directory. The test_hooks.py can also be moved into test_hooks/ directory.

[zhouzaida]

Agree to refactor the test_hooks directory. The test_hooks.py can also be moved into test_hooks/ directory.

Got it, I will refactor the unit test of hooks in the next PR.