Interner<String> pool = Interners.newStrongInterner();
    assertThat(pool.intern(canonical)).isSameInstanceAs(canonical);
    assertThat(pool.intern(not)).isSameInstanceAs(canonical);
  }

  public void testStrong_null() {
    Interner<String> pool = Interners.newStrongInterner();
    assertThrows(NullPointerException.class, () -> pool.intern(null));
  }

  public void testStrong_builder() {
    int concurrencyLevel = 42;