* @param instance the component instance
         * @param initializer the initializer function (can be null)
         * @param container the container instance for dependency injection
         */
        protected ComponentDef(final T instance, final Consumer<T> initializer, final StandardCrawlerContainer container) {
            this.instance = instance;
            this.initializer = initializer;

    void testGetInstanceWithoutSetInstance() {
        // Test getInstance when no instance has been set
        // Should default to System.err
        LogStream instance = LogStream.getInstance();
        assertNotNull(instance);

        // Getting instance again should return the same instance
        LogStream instance2 = LogStream.getInstance();
        assertSame(instance, instance2);
    }

    @Test

    // Use reflection to reset the singleton instance between tests
    @BeforeEach
    @AfterEach
    void resetSingleton() {
        try {
            Field instance = SingletonContext.class.getDeclaredField("INSTANCE");
            instance.setAccessible(true);
            instance.set(null, null);
        } catch (NoSuchFieldException | IllegalAccessException e) {

        byte[] buffer = new byte[] { (byte) 0xff, (byte) 0xff, 0, 0, 0, 0, 0, 0 };
        SmbComWriteAndXResponse instance = new SmbComWriteAndXResponse(config);

        // When
        int result = instance.readParameterWordsWireFormat(buffer, 0);

        // Then
        assertEquals(8, result);
        assertEquals(0xffffL, instance.getCount());
    }

    /**
     * Test of readParameterWordsWireFormat with zero count
     */

         * @param status The status to set.
         * @return This ApiResponse instance.
         */
        public ApiResponse status(final Status status) {
            this.status = status.getId();
            return this;
        }

        /**
         * Returns a new ApiResult instance with this ApiResponse.
         * @return A new ApiResult instance.
         */
        public ApiResult result() {

But we want to be able to parameterize that fixed content.

## A "callable" instance { #a-callable-instance }

In Python there's a way to make an instance of a class a "callable".

Not the class itself (which is already a callable), but an instance of that class.

To do that, we declare a method `__call__`:

{* ../../docs_src/dependencies/tutorial011_an_py39.py hl[12] *}

      @ParametricNullness T instance) {
    return new SupplierOfInstance<>(instance);
  }

  private static final class SupplierOfInstance<T extends @Nullable Object>
      implements Supplier<T>, Serializable {
    @ParametricNullness final T instance;

    SupplierOfInstance(@ParametricNullness T instance) {
      this.instance = instance;
    }

    @Override
    @ParametricNullness
    public T get() {

     * <p>
     * If a root package is specified at instance construction, the specified class name is interpreted as a relative name from the root package.
     * </p>
     *
     * @param className the class name
     * @return <code>true</code> if the class file exists in the resources handled by this instance
     */
    boolean isExistClass(final String className);

      for (Invokable<?, ?> factory : getFactoriesToTest()) {
        Object instance = instantiate(factory);
        if (instance != null
            && packagesToTest.contains(Reflection.getPackageName(instance.getClass()))) {
          try {
            nullPointerTester.testAllPublicInstanceMethods(instance);
          } catch (AssertionError e) {

Pero queremos poder parametrizar ese contenido fijo.

## Una *instance* "callable"

En Python hay una forma de hacer que una instance de una clase sea un "callable".

No la clase en sí (que ya es un callable), sino una instance de esa clase.

Para hacer eso, declaramos un método `__call__`:

{* ../../docs_src/dependencies/tutorial011_an_py39.py hl[12] *}