c = entries.get(2);
      }
    }
  }

  @CollectionSize.Require(ZERO)
  public void testEmptyMapFirst() {
    assertThrows(NoSuchElementException.class, () -> navigableMap.firstKey());
  }

  @CollectionSize.Require(ZERO)
  public void testEmptyMapLast() {
    assertThrows(NoSuchElementException.class, () -> assertNull(navigableMap.lastKey()));
  }

  @CollectionSize.Require(ONE)

import static com.google.common.escape.testing.EscaperAsserts.assertUnescaped;
import static com.google.common.escape.testing.EscaperAsserts.assertUnicodeEscaping;
import static com.google.common.net.ReflectionFreeAssertThrows.assertThrows;
import static com.google.common.truth.Truth.assertThat;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Preconditions;
import com.google.common.escape.UnicodeEscaper;

    Set<Integer> nodes = network.nodes();
    assertThrows(UnsupportedOperationException.class, () -> nodes.add(N2));
    addNode(N1);
    assertThat(network.nodes()).containsExactlyElementsIn(nodes);
  }

  @Override
  @Test
  public void edges_checkReturnedSetMutability() {
    assume().that(graphIsMutable()).isTrue();

    Set<String> edges = network.edges();
    assertThrows(UnsupportedOperationException.class, () -> edges.add(E12));

  }

  public void testSampleVariance() {
    assertThrows(IllegalStateException.class, () -> emptyAccumulator.sampleVariance());
    assertThrows(
        IllegalStateException.class, () -> emptyAccumulatorByAddAllEmptyIterable.sampleVariance());
    assertThrows(
        IllegalStateException.class, () -> emptyAccumulatorByAddAllEmptyStats.sampleVariance());

  }

  public void testPearsonsCorrelationCoefficient() {
    assertThrows(
        IllegalStateException.class, () -> EMPTY_PAIRED_STATS.pearsonsCorrelationCoefficient());
    assertThrows(
        IllegalStateException.class, () -> ONE_VALUE_PAIRED_STATS.pearsonsCorrelationCoefficient());
    assertThrows(
        IllegalStateException.class,

    Set<Integer> nodes = network.nodes();
    assertThrows(UnsupportedOperationException.class, () -> nodes.add(N2));
    addNode(N1);
    assertThat(network.nodes()).containsExactlyElementsIn(nodes);
  }

  @Override
  @Test
  public void edges_checkReturnedSetMutability() {
    assume().that(graphIsMutable()).isTrue();

    Set<String> edges = network.edges();
    assertThrows(UnsupportedOperationException.class, () -> edges.add(E12));

    assertThat(setToTest).isEqualTo(setToTest);
    assertThrows(IllegalStateException.class, () -> setToTest.equals(wrappedSet));
    assertThrows(IllegalStateException.class, () -> setToTest.equals(copyOfWrappedSet));
    assertThrows(IllegalStateException.class, () -> setToTest.equals(copyOfModifiedSet));
    assertThrows(IllegalStateException.class, () -> wrappedSet.equals(setToTest));

  }

  public void testToOptionalNull() {
    Stream<@Nullable Object> stream = Stream.of((Object) null);
    assertThrows(NullPointerException.class, () -> stream.collect(toOptional()));
  }

  public void testToOptionalMultiple() {
    IllegalArgumentException expected =
        assertThrows(IllegalArgumentException.class, () -> Stream.of(1, 2).collect(toOptional()));
    assertThat(expected.getMessage()).contains("1, 2");
  }

    assertEquals(-1, iterator.previousIndex());
    assertThrows(NoSuchElementException.class, () -> iterator.next());
    assertThrows(NoSuchElementException.class, () -> iterator.previous());
    assertThrows(UnsupportedOperationException.class, () -> iterator.remove());
    assertThrows(UnsupportedOperationException.class, () -> iterator.set("a"));
    assertThrows(UnsupportedOperationException.class, () -> iterator.add("a"));
  }

    verify(true);
  }

  public void testVerify_simple_failure() {
    assertThrows(VerifyException.class, () -> verify(false));
  }

  public void testVerify_simpleMessage_success() {
    verify(true, "message");
  }

  public void testVerify_simpleMessage_failure() {
    VerifyException expected = assertThrows(VerifyException.class, () -> verify(false, "message"));