[Enhance] Add phase for test.py

[liuyanyi]

Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily get feedback. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.

Motivation

Add phase for test.py

For example, commonly we need coco val for valdation and test, if use coco test to evaluate online, we need modify test dataloader and test evaluator.

After this pr, the phase for test can be specifiy and we can simplify the configs need online evaluate such as coco and dota.

runner.val() can't use because tta only support test.

TODO

• Clean test code after fully test.
• How to support coco evaluate with train? should we modify the val evaluator?

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the backward compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit tests to ensure the correctness.
3. If the modification has a potential influence on downstream projects, this PR should be tested with downstream projects, like MMDetection or MMClassification.
4. The documentation has been modified accordingly, like docstring or example tutorials.