assertEquals("Ordering.natural()", comparator.toString());
  }

  public void testFrom() {
    Ordering<String> caseInsensitiveOrdering = Ordering.from(String.CASE_INSENSITIVE_ORDER);
    assertEquals(0, caseInsensitiveOrdering.compare("A", "a"));
    assertTrue(caseInsensitiveOrdering.compare("a", "B") < 0);
    assertTrue(caseInsensitiveOrdering.compare("B", "a") > 0);

 * <li>version components in the text can be digits or strings,</li>
 * <li>strings are checked for well-known qualifiers and the qualifier ordering is used for version ordering.
 *     Well-known qualifiers (case insensitive) are:<ul>
 *     <li><code>alpha</code> or <code>a</code></li>
 *     <li><code>beta</code> or <code>b</code></li>
 *     <li><code>milestone</code> or <code>m</code></li>
 *     <li><code>rc</code> or <code>cr</code></li>

  }

  public void testToImmutableSortedMap() {
    Collector<Entry<String, Integer>, ?, ImmutableSortedMap<String, Integer>> collector =
        ImmutableSortedMap.toImmutableSortedMap(
            String.CASE_INSENSITIVE_ORDER, Entry::getKey, Entry::getValue);
    BiPredicate<ImmutableSortedMap<String, Integer>, ImmutableSortedMap<String, Integer>>
        equivalence =
            Equivalence.equals()

    assertEquals("[1, 2, 3, 5, 10, 15, 20]", table.columnKeySet().toString());
  }

  public void testColumnKeySet_isSortedWithRealComparator() {
    table =
        create(
            String.CASE_INSENSITIVE_ORDER,
            Ordering.<Integer>natural().reverse(),
            "a",
            2,
            'X',
            "a",
            2,
            'X',
            "b",
            3,

        checkVersionsEqual("1a1", "1-alpha-1");
        checkVersionsEqual("1b2", "1-beta-2");
        checkVersionsEqual("1m3", "1-milestone-3");

        // case insensitive
        checkVersionsEqual("1X", "1x");
        checkVersionsEqual("1A", "1a");
        checkVersionsEqual("1B", "1b");
        checkVersionsEqual("1M", "1m");
        checkVersionsEqual("1Cr", "1Rc");

   * then comparing those results using {@code this}. For example, to compare objects by their
   * string forms, in a case-insensitive manner, use:
   *
   * <pre>{@code
   * Ordering.from(String.CASE_INSENSITIVE_ORDER)
   *     .onResultOf(Functions.toStringFunction())
   * }</pre>
   *
   * <p><b>Java 8+ users:</b> Use {@code Comparator.comparing(function, thisComparator)} instead

    private static final String PDF_DATE = "pdf_date";

    private static final Pattern EMAIL_ADDRESS_PATTERN =
            Pattern.compile("[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,6}", Pattern.CASE_INSENSITIVE);

    private static LoadingCache<String, Long> resourceHashCache =
            CacheBuilder.newBuilder().maximumSize(1000).expireAfterWrite(10, TimeUnit.MINUTES).build(new CacheLoader<String, Long>() {

  }

  public void testToImmutableSortedSet_customComparator() {
    Collector<String, ?, ImmutableSortedSet<String>> collector =
        ImmutableSortedSet.toImmutableSortedSet(String.CASE_INSENSITIVE_ORDER);
    BiPredicate<ImmutableSortedSet<String>, ImmutableSortedSet<String>> equivalence =
        (set1, set2) ->
            set1.equals(set2)
                && set1.asList().equals(set2.asList())

Then, when you create an instance of that `Settings` class (in this case, in the `settings` object), Pydantic will read the environment variables in a case-insensitive way, so, an upper-case variable `APP_NAME` will still be read for the attribute `app_name`.

    assertEquals("[1, 2, 3, 5, 10, 15, 20]", table.columnKeySet().toString());
  }

  public void testColumnKeySet_isSortedWithRealComparator() {
    table =
        create(
            String.CASE_INSENSITIVE_ORDER,
            Ordering.<Integer>natural().reverse(),
            "a",
            2,
            'X',
            "a",
            2,
            'X',
            "b",
            3,