task: Improve the test case coverage of [discovery] module to 70% #6503
Description
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The test case coverage of [discovery] module is 31.23%, We need to go up to 70% to improve the robustness and stability of our code.
[discovery]模块的测试用例覆盖率为31.23%，我们需要提高到70%，以提高代码的健壮性和稳定性。
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You can get some help from:
https://seata.apache.org/docs/developers/contributor-guide/test-coverage-guide_dev
https://seata.apache.org/blog/how-to-write-unit-tests