fix: race-condition problem on testhelper (#5)

[karupanerura]

switch to context based log writer override

[glassonion1]

Thanks for the pull request. I have a question.

It seemed that the SetContextConfig function was only used in the test.
Are you aware that ContextConfig will only be used for testing?

Please tell me what kind of problem occurred in the test.

If it's a test-specific issue, I think it's better to fix it so that it doesn't affect the production code.