class PHPUnit_Framework_Constraint_IsJson

class PHPUnit_Framework_Constraint_IsJson extends PHPUnit_Framework_Constraint {

  /**
   * Evaluates the constraint for parameter $other. Returns TRUE if the
   * constraint is met, FALSE otherwise.
   *
   * @param mixed $other Value or object to evaluate.
   * @return bool
   */
  protected function matches($other) {
    json_decode($other);
    if (json_last_error()) {
      return FALSE;
    }
    return TRUE;
  }

  /**
   * Returns the description of the failure
   *
   * The beginning of failure messages is "Failed asserting that" in most
   * cases. This method should return the second part of that sentence.
   *
   * @param  mixed $other Evaluated value or object.
   * @return string
   */
  protected function failureDescription($other) {
    json_decode($other);
    $error = PHPUnit_Framework_Constraint_JsonMatches_ErrorMessageProvider::determineJsonError(json_last_error());
    return sprintf('%s is valid JSON (%s)', PHPUnit_Util_Type::shortenedExport($other), $error);
  }

  /**
   * Returns a string representation of the constraint.
   *
   * @return string
   */
  public function toString() {
    return 'is valid JSON';
  }

}