@PublicAPI(usage = ACCESS)
    public JavaPackage getPackage(String packageName) {
        return getValue(tryGetPackage(packageName), "This package does not contain any sub package '%s'", packageName);
    }
@Test
    public void function_GET_CLASSES() {
        JavaPackage defaultPackage = importDefaultPackage(Object.class, String.class, Collection.class);

        Iterable<JavaClass> classes = GET_CLASSES.apply(defaultPackage.getPackage("java.lang"));

        assertThatTypes(classes).contain(Object.class, String.class);
        for (JavaClass javaClass : classes) {
            assertThat(javaClass.getPackageName()).startsWith("java.lang");
        }
    }