return NO_CHARS;
          }
        };
    EscaperAsserts.assertBasic(escaper);
    assertEquals("<tab>Fish <and> Chips<newline>", escaper.escape("\tFish & Chips\n"));

    // Verify that everything else is left unescaped.
    String safeChars = "\0\u0100\uD800\uDC00\uFFFF";
    assertEquals(safeChars, escaper.escape(safeChars));

    // Ensure that Unicode escapers behave correctly wrt badly formed input.

 * individual {@code char} values, it is not safe to assume that {@code escape(s)} is equivalent to
 * {@code escape(s.substring(0, n)) + escape(s.substring(n))} for arbitrary {@code n}. This is
 * because of the possibility of splitting a surrogate pair. The only case in which it is safe to
 * escape strings and concatenate the results is if you can rule out this possibility, either by

   *
   * @param escaper the instance to be wrapped
   * @return a UnicodeEscaper with the same behavior as the given instance
   * @throws NullPointerException if escaper is null
   * @throws IllegalArgumentException if escaper is not a UnicodeEscaper or a CharEscaper
   */
  static UnicodeEscaper asUnicodeEscaper(Escaper escaper) {
    checkNotNull(escaper);
    if (escaper instanceof UnicodeEscaper) {

   *
   * <p>An escaper is expected to be able to deal with any {@code char} value, so this method should
   * not throw any exceptions.
   *
   * @param c the character to escape if necessary
   * @return the replacement characters, or {@code null} if no escaping was needed
   */
  @CheckForNull
  protected abstract char[] escape(char c);

  /**

    assertUnicodeEscaping(e, "%F4%8F%BF%BF", '\uDBFF', '\uDFFF');

    assertEquals("", e.escape(""));
    assertEquals("safestring", e.escape("safestring"));
    assertEquals("embedded%00null", e.escape("embedded\0null"));
    assertEquals("max%EF%BF%BFchar", e.escape("max\uffffchar"));
  }

  // Helper to assert common expected behaviour of uri escapers.

            return NO_CHARS;
          }
        };
    EscaperAsserts.assertBasic(escaper);
    assertEquals("<tab>Fish <and> Chips<newline>", escaper.escape("\tFish & Chips\n"));

    // Verify that everything else is left unescaped.
    String safeChars = "\0\u0100\uD800\uDC00\uFFFF";
    assertEquals(safeChars, escaper.escape(safeChars));

    // Ensure that Unicode escapers behave correctly wrt badly formed input.

    Escaper escaper = Escapers.nullEscaper();
    EscaperAsserts.assertBasic(escaper);
    String s = "\0\n\t\\az09~\uD800\uDC00\uFFFF";
    assertEquals("null escaper should have no effect", s, escaper.escape(s));
  }

  public void testBuilderInitialStateNoReplacement() {
    // Unsafe characters aren't modified by default (unsafeReplacement == null).

  }

  private static final Escaper XML_ESCAPER;
  private static final Escaper XML_CONTENT_ESCAPER;
  private static final Escaper XML_ATTRIBUTE_ESCAPER;

  static {
    Escapers.Builder builder = Escapers.builder();
    // The char values \uFFFE and \uFFFF are explicitly not allowed in XML
    // (Unicode code points above \uFFFF are represented via surrogate pairs
    // which means they are treated as pairs of safe characters).

    assertUnicodeEscaping(e, "%F4%8F%BF%BF", '\uDBFF', '\uDFFF');

    // simple string tests
    assertEquals("", e.escape(""));
    assertEquals("safestring", e.escape("safestring"));
    assertEquals("embedded%00null", e.escape("embedded\0null"));
    assertEquals("max%EF%BF%BFchar", e.escape("max\uffffchar"));
  }

  /** Tests the various ways that the space character can be handled */
  public void testPlusForSpace() {

import static org.junit.Assert.assertThat;

import org.junit.Test;

/**
 * @author shinsuke
 *
 */
public class JsonUtilTest {
    @Test
    public void escape() {
        assertThat(JsonUtil.escape("abc123あア亜"), is("abc123あア亜"));
        assertThat(JsonUtil.escape("\\\"/\b\t\n\f\r\0"), is("\\\\\\\"\\/\\b\\t\\n\\f\\r\\u0000"));
    }