def METHOD_NAME():
    def getter(key: str):
        return key
    registry = ExternalRegistry(getter, "backbones", "test_provider")
    assert registry.get("testing")() == "testing"
    available = registry.available_keys()
    assert len(available) == 1
    assert "test_provider" in available[0]
    registry = ExternalRegistry(getter, "backbones", ["test_provider_1", "test_provider_2"])
    assert "test_provider_1, test_provider_2" in registry.available_keys()[0]
    registry = ExternalRegistry(getter, "backbones")
    assert len(registry.available_keys()) == 0