We have a few types that use static singletons to store "global" instances - configuration, service registry, metrics.

Introduce a new common type io.helidon.common.GlobalInstances to handle such singletons, that has a capability to be cleared.
This is a temporary solution - we want to move all instances to ServiceRegisty, and use the GlobalServiceRegistry to obtain them instead, as service registry can manage lifecycle and provides basic inversion of control, to obtain config etc.

Context approach was not working nicely, as you may access the global from a custom context (such as a server request), and then it would not be a global.
For testing purposes, it would be really great to have these instances bound to Helidon Context, instead of as singletons.
Proposal:
create ContextValue in io.helidon.common.context that would take care of this
~~register the values in either the global config (keeping current behavior of global singleton at runtime), or with a current context (or its parent hierarchy) that has an ID starting with test-, to support test-scoped singletons
create an extension for testing that runs everything (before all, after all, each test method, constructor) in Helidon and create a new context for each test class being executed (i.e. all methods within a class share the same context)
modify existing "globals" to use the new approach