StringBuilder builder = new StringBuilder();
    Writer writer = new AppendableWriter(builder);

    writer.write("Hi");
    writer.close();

    assertThrows(IOException.class, () -> writer.write(" Greg"));

    assertThrows(IOException.class, () -> writer.flush());

    // close()ing already closed writer is allowed
    writer.close();
  }

        // Count how many registrations this affects
        int affectedRegistrations = 0;
        for (MockRegistration reg : registrations.values()) {
            if (reg.shareName.equalsIgnoreCase(resourceName) || reg.serverAddress.equals(resourceName)) {
                affectedRegistrations++;
            }
        }

    }

    /**
     * Generates a unique registration ID.
     *
     * @return a unique registration identifier
     */
    private String generateRegistrationId() {
        return "REG-" + System.currentTimeMillis() + "-" + Integer.toHexString(System.identityHashCode(this));
    }

    /**
     * Gets the next sequence number for this registration.
     *
     * @return the next sequence number