* configuration which can be declared against.
     *
     * @return {@code true} if so; {@code false} otherwise
     */
    default boolean isDeclarableByExtension() {
        return isDeclarableByExtension(this);
    }

    /**
     * Returns the role used to create this configuration and set its initial allowed usage.
     */
    ConfigurationRole getRoleAtCreation();

    /**

    void setup() {
        configurationMock.isDeclarableByExtension() >> true
        configurationContainerStub.findByName(TEST_CONF_NAME) >> configurationMock
        configurationContainerStub.getByName(TEST_CONF_NAME) >> configurationMock

        return project.getConfigurations().stream()
            .map(ConfigurationInternal.class::cast)
            .filter(c -> c.isDeclarableByExtension())
            .map(ConfigurationDetails::of);
    }

        Set<Configuration> filteredConfigurations = new HashSet<>();
        for (Configuration configuration : Objects.requireNonNull(getTaskConfigurations())) {
            if (((ConfigurationInternal)configuration).isDeclarableByExtension()) {
                filteredConfigurations.add(configuration);
            }
        }
        return filteredConfigurations;
    }

    @Internal