* will be read from or set for consumption in the Maven build lifecycle.
     *
     * The source indicates whether the property is:
     * - Set by Maven itself at startup (SYSTEM_PROPERTIES)
     * - Configured by users through external means like CLI options (USER_PROPERTIES)
     * - Defined in the project's POM file (MODEL)
     *

  @SuppressWarnings({
    "SelfEquals", // TODO(cpovirk): Consider using EqualsTester from Guava.
    "UndefinedEquals", // Comparisons of an object to itself *are* defined.
  })
  public void testEquals_self() {
    assertTrue("An Object should be equal to itself.", collection.equals(collection));
  }

  // Comparisons to null *are* defined.
  @SuppressWarnings("UndefinedEquals")
  public void testEquals_null() {

    Contains Guava's com.google.common.util.concurrent.ListenableFuture class,
    without any of its other classes -- but is also available in a second
    "version" that omits the class to avoid conflicts with the copy in Guava
    itself. The idea is:

    - If users want only ListenableFuture, they depend on listenablefuture-1.0.

    - If users want all of Guava, they depend on guava, which, as of Guava
    27.0, depends on

 *     .addEqualityGroup(new User("page"), new User("page"))
 *     .addEqualityGroup(new User("sergey"))
 *     .testEquals();
 * </pre>
 *
 * <p>This tests:
 *
 * <ul>
 *   <li>comparing each object against itself returns true
 *   <li>comparing each object against null returns false
 *   <li>comparing each object against an instance of an incompatible class returns false

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] *}

  @SuppressWarnings({
    "SelfEquals", // TODO(cpovirk): Consider using EqualsTester from Guava.
    "UndefinedEquals", // Comparisons of an object to itself *are* defined.
  })
  public void testEquals_self() {
    assertTrue("An Object should be equal to itself.", collection.equals(collection));
  }

  // Comparisons to null *are* defined.
  @SuppressWarnings("UndefinedEquals")
  public void testEquals_null() {

 *       other tests. We want to exclude the other tests (which Android can't handle) while
 *       continuing to run {@code FooTest} itself. This is exactly what happens with {@code
 *       AndroidIncompatible}. But I'm not sure what would happen if we annotated the {@code
 *       suite()} method with {@code Suppress}. Would {@code FooTest} itself be suppressed, too?

       * since the Equivalence base type now implements this logic itself
       */
      assertTrue(item + " must be inequivalent to null", !equivalence.equivalent(item, null));
      assertTrue("null must be inequivalent to " + item, !equivalence.equivalent(null, item));
      assertTrue(item + " must be equivalent to itself", equivalence.equivalent(item, item));
      assertEquals(

 *     .addEqualityGroup(new User("page"), new User("page"))
 *     .addEqualityGroup(new User("sergey"))
 *     .testEquals();
 * </pre>
 *
 * <p>This tests:
 *
 * <ul>
 *   <li>comparing each object against itself returns true
 *   <li>comparing each object against null returns false
 *   <li>comparing each object against an instance of an incompatible class returns false

import (
	"compress/flate"
	"errors"
	"io"
	"sync"
)

// A Compressor returns a new compressing writer, writing to w.
// The WriteCloser's Close method must be used to flush pending data to w.
// The Compressor itself must be safe to invoke from multiple goroutines
// simultaneously, but each returned writer will be used only by
// one goroutine at a time.
type Compressor func(w io.Writer) (io.WriteCloser, error)