assertArgumentNotNull("reader", reader);
        this.reader = reader;
    }

    @Override
    public boolean hasNext() {
        if (line == EMPTY) {
            line = ReaderUtil.readLine(reader);
        }
        return line != null;
    }

    @Override
    public String next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }

Probablemente quieras probar el proveedor externo una vez, pero no necesariamente llamarlo para cada test que se realice.

En este caso, puedes sobrescribir la dependencia que llama a ese proveedor y usar una dependencia personalizada que devuelva un usuario de prueba, solo para tus tests.

### Usa el atributo `app.dependency_overrides`

    }

    @Test
    @DisplayName("readLine(): reads until newline and handles CRLF")
    void readLine_reads() throws Exception {
        SmbRandomAccessFile raf = spy(newInstance("r", false, false, false));
        // Sequence: 'a','b','\r','\n','c','\n'
        when(raf.read()).thenReturn((int) 'a', (int) 'b', (int) '\r', (int) '\n');
        assertEquals("ab", raf.readLine());

  @Override
  float readFloat();

  @CanIgnoreReturnValue // to skip some bytes
  @Override
  double readDouble();

  @CanIgnoreReturnValue // to skip a line
  @Override
  @Nullable String readLine();

  @CanIgnoreReturnValue // to skip a field
  @Override
  String readUTF();

        } else {
          System.err.println(callback.prompt)
          callback.password =
            System.`in`
              .bufferedReader()
              .readLine()
              .toCharArray()
        }
      } else {
        throw UnsupportedCallbackException(callback)
      }
    }
  }
}

fun main() {
  YubikeyClientAuth().run()

     */
    @Override
    public void run() {
        boolean running = true;
        while (running) {
            try {
                final String line = br.readLine();
                if (line == null) {
                    running = false;
                } else {
                    if (logger.isDebugEnabled()) {
                        logger.debug(line);
                    }

         */
        @Override
        public void run() {
            for (;;) {
                try {
                    final String line = br.readLine();
                    if (line == null) {
                        break;
                    }
                    if (logger.isDebugEnabled()) {
                        logger.debug(line);
                    }

        try (BufferedReader reader = new BufferedReader(new InputStreamReader(in, Constants.UTF_8))) {
            long id = 0;
            String line = null;
            while ((line = reader.readLine()) != null) {
                // Remove comments
                final String replacedLine = line.replaceAll("#.*$", StringUtil.EMPTY).trim();

                // Skip empty lines or comment lines

                    new BufferedReader(new InputStreamReader(new FileInputStream(tempFile.toFile()), Constants.CHARSET_UTF_8))) {
                String line;
                while ((line = reader.readLine()) != null) {
                    lines.add(line);
                }
            }

            assertFalse("File should contain lines", lines.isEmpty());

            // Verify content structure

        if (read(tmp, 0, 8) < 0) {
            throw new SmbException("EOF");
        }
        return Encdec.dec_doublebe(tmp, 0);
    }

    @Override
    public final String readLine() throws SmbException {
        final StringBuilder input = new StringBuilder();
        int c = -1;
        boolean eol = false;

        while (!eol) {
            switch (c = read()) {
            case -1: