### Question:
BiCollection { @Override public boolean equals(Object obj) { if (obj instanceof BiCollection<?, ?>) { BiCollection<?, ?> that = (BiCollection<?, ?>) obj; return entries.equals(that.entries); } return false; } private  BiCollection(Collection<? extends Entry<L, R>> underlying); @SuppressWarnings("unchecked") static BiCollection<L, R> of(); static BiCollection<L, R> of(L left, R right); static BiCollection<L, R> of(L left1, R right1, L left2, R right2); static BiCollection<L, R> of(L left1, R right1, L left2, R right2, L left3, R right3); static BiCollection<L, R> of(
      L left1, R right1, L left2, R right2, L left3, R right3, L left4, R right4); static BiCollection<L, R> of(
      L left1, R right1, L left2, R right2, L left3, R right3, L left4, R right4, L left5, R right5); static Collector<T, ?, BiCollection<L, R>> toBiCollection(
      Function<? super T, ? extends L> leftFunction,
      Function<? super T, ? extends R> rightFunction); int size(); BiStream<L, R> stream(); @Override int hashCode(); @Override boolean equals(Object obj); @Override String toString();  }### Answer:
@Test public void testEquals() { new EqualsTester() .addEqualityGroup(BiCollection.of(), BiCollection.of()) .addEqualityGroup(BiCollection.of("a", 1), BiCollection.of("a", 1)) .addEqualityGroup(BiCollection.of("a", 2)) .addEqualityGroup(BiCollection.of("b", 1)) .addEqualityGroup(BiCollection.of("a", 1, "a", 1)) .testEquals(); }