doTestCollapseWithNoChange("");
    doTestCollapseWithNoChange("x");
    doTestCollapseWithNoChange("xx");
  }

  private void doTestCollapse(String in, String out) {
    // Try a few different matchers which all match '-' and not 'x'
    // Try replacement chars that both do and do not change the value.
    for (char replacement : new char[] {'_', '-'}) {
      String expected = out.replace('_', replacement);

    doTestCollapseWithNoChange("");
    doTestCollapseWithNoChange("x");
    doTestCollapseWithNoChange("xx");
  }

  private void doTestCollapse(String in, String out) {
    // Try a few different matchers which all match '-' and not 'x'
    // Try replacement chars that both do and do not change the value.
    for (char replacement : new char[] {'_', '-'}) {
      String expected = out.replace('_', replacement);

    // It turns out that creating a new String is usually as fast, or faster
    // than wrapping cbuf in a light-weight CharSequence.
    target.append(new String(cbuf, off, len));
  }

  /*
   * Override a few functions for performance reasons to avoid creating unnecessary strings.
   */

  @Override
  public void write(int c) throws IOException {
    checkNotClosed();
    target.append((char) c);
  }

  @Override

 *
 * <p>The simplest use case is:
 *
 * <pre>
 * new EqualsTester().addEqualityGroup(foo).testEquals();
 * </pre>
 *
 * <p>This tests {@code foo.equals(foo)}, {@code foo.equals(null)}, and a few other operations.
 *
 * <p>For more extensive testing, add multiple equality groups. Each group should contain objects
 * that are equal to each other but unequal to the objects in any other group. For example:
 *
 * <pre>

 *
 * <p>The simplest use case is:
 *
 * <pre>
 * new EqualsTester().addEqualityGroup(foo).testEquals();
 * </pre>
 *
 * <p>This tests {@code foo.equals(foo)}, {@code foo.equals(null)}, and a few other operations.
 *
 * <p>For more extensive testing, add multiple equality groups. Each group should contain objects
 * that are equal to each other but unequal to the objects in any other group. For example:
 *
 * <pre>

) : Lockable {
  private var nextQueueName = 10000
  private var coordinatorWaiting = false
  private var coordinatorWakeUpAt = 0L

  /**
   * When we need a new thread to run tasks, we call [Backend.execute]. A few microseconds later we
   * expect a newly-started thread to call [Runnable.run]. We shouldn't request new threads until
   * the already-requested ones are in service, otherwise we might create more threads than we need.
   *

        // Test too many fields
        bean.setCronExpression("* * * * * * * *");
        violations = validator.validate(bean);
        assertFalse(violations.isEmpty());

        // Test too few fields
        bean.setCronExpression("* * *");
        violations = validator.validate(bean);
        assertFalse(violations.isEmpty());
    }

    // Test validation with groups

                + expected
                + ", actual = "
                + actual);
      }
    }

    if (expectedIter.hasNext() || actualIter.hasNext()) {
      // actual either had too few or too many elements
      fail(
          "contents were not equal and in the same order: "
              + "expected = "
              + expected
              + ", actual = "
              + actual);
    }

 * across the key-value mappings in the order they were added to the multimap.
 *
 * <p>The iteration ordering of the collections generated by {@code keySet}, {@code keys}, and
 * {@code asMap} has a few subtleties. As long as the set of keys remains unchanged, adding or
 * removing mappings does not affect the key iteration order. However, if you remove all values

import java.util.List;
import java.util.Spliterator;
import java.util.Spliterators;
import org.jspecify.annotations.Nullable;

/**
 * A {@link Collection} whose contents will never change, and which offers a few additional
 * guarantees detailed below.
 *
 * <p><b>Warning:</b> avoid <i>direct</i> usage of {@link ImmutableCollection} as a type (just as