### Question:
DefaultExtensionRegistry implements ExtensionRegistry { @Override public Set<String> getQuarkusCoreVersions() { return registry.getCoreVersions().keySet().stream().map(ComparableVersion::toString).collect( Collectors.toCollection(LinkedHashSet::new)); } DefaultExtensionRegistry(Registry registry); static DefaultExtensionRegistry fromURLs(Collection<URL> urls); static DefaultExtensionRegistry fromPlatform(QuarkusPlatformDescriptor platform); @Override Set<String> getQuarkusCoreVersions(); @Override Set<Extension> getExtensionsByCoreVersion(String version); @Override Set<Extension> list(String quarkusCore, String keyword); @Override ExtensionInstallPlan planInstallation(String quarkusCore, Collection<String> keywords); Registry getRegistry();  }### Answer:
@Test void shouldReturnFourQuarkusCoreVersions() { assertThat(extensionRegistry.getQuarkusCoreVersions()).containsExactly( "1.6.0.Final", "1.5.2.Final", "1.3.2.Final"); }