• I have searched the issues of this repository and believe that this is not a duplicate.
• I have checked the FAQ of this repository and believe that this is not a duplicate.

The tests are not idempotent and fails if run twice in the same JVM, because each of the tests pollutes state shared among tests:

• dubbo-common,org.apache.dubbo.common.extension.ExtensionLoaderTest.test_replaceExtension_Adaptive
• dubbo-common,org.apache.dubbo.common.extension.ExtensionLoaderTest.test_AddExtension
• dubbo-common,org.apache.dubbo.common.extension.ExtensionLoaderTest.test_replaceExtension

Environment

• Dubbo version: Branched from master
• Operating System version: macOS 10.15.6
• Java version: 1.8.0_151

Steps to reproduce this issue

1. Run unit test ExtensionLoaderTest.test_replaceExtension_Adaptive twice in the same JVM.
2. Run unit test ExtensionLoaderTest.test_AddExtension twice in the same JVM.
3. Run unit test ExtensionLoaderTest.test_replaceExtension twice in the same JVM.

Expected Result

The tests don't pollute shared states and pass when running twice in the same JVM.

Actual Result

The tests fail when running twice in the same JVM.