[igorbernstein2]

Summary

When session_load == 0 across all scopes, ClientConfigurationManager.normalizeConfig clears session_configuration, resulting in an empty ChannelPoolConfiguration.getDefaultInstance().

This change updates SwitchingChannelPool to treat an empty ChannelPoolConfiguration (config.equals(ChannelPoolConfiguration.getDefaultInstance())) as disabled:

• Delegates to a NoopChannelPool when disabled, which creates no underlying channels and immediately fails newStream with Status.UNAVAILABLE.
• Transitions cleanly between disabled (NoopChannelPool) and enabled (ChannelPoolDpImpl / FallbackChannelPool / SingleChannelPool) on updateConfig via replaceChannelPool(createDelegate()), shutting down the active pool's channels when disabled.

[gemini-code-assist]

Code Review

This pull request introduces support for disabling the channel pool in SwitchingChannelPool by utilizing a new NoopChannelPool when the configuration is empty or default. It refactors delegate creation and config updates to seamlessly transition between enabled and disabled states, and adds a comprehensive test suite in SwitchingChannelPoolTest. The review feedback suggests a minor improvement in the test code to avoid reusing the same ArgumentCaptor instance across different mock verifications, which can lead to fragile tests.

[gemini-code-assist]

Reusing the same ArgumentCaptor instance (statusCaptor) across different mock verifications (streamListener and secondListener) is a code smell and can lead to fragile tests or unexpected behavior if the verifications are reordered or if multiple interactions occur. It is safer and cleaner to use a separate ArgumentCaptor instance for the second verification.

Suggested change

	verify(secondListener).onClose(statusCaptor.capture(), any(Metadata.class));
	assertThat(statusCaptor.getValue().getCode()).isEqualTo(Status.Code.UNAVAILABLE);
	ArgumentCaptor<Status> secondStatusCaptor = ArgumentCaptor.forClass(Status.class);
	verify(secondListener).onClose(secondStatusCaptor.capture(), any(Metadata.class));
	assertThat(secondStatusCaptor.getValue().getCode()).isEqualTo(Status.Code.UNAVAILABLE);