@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();
}