ImmutableBiMap.copyOf(map);
      fail();
    } catch (IllegalArgumentException expected) {
      assertThat(expected.getMessage()).containsMatch("1|2");
      // We don't specify which of the two dups should be reported.
    }
  }

  public void testToImmutableBiMap() {
    Collector<Entry<String, Integer>, ?, ImmutableBiMap<String, Integer>> collector =
        ImmutableBiMap.toImmutableBiMap(Entry::getKey, Entry::getValue);

      ImmutableBiMap.copyOf(map);
      fail();
    } catch (IllegalArgumentException expected) {
      assertThat(expected.getMessage()).containsMatch("1|2");
      // We don't specify which of the two dups should be reported.
    }
  }

  // TODO(b/172823566): Use mainline testToImmutableBiMap once CollectorTester is usable to java7.
  public void testToImmutableBiMap_java7_combine() {
    ImmutableBiMap.Builder<String, Integer> zis =