Java: How do I unit test a method that creates and manipulates a file within the scope of the method?

I'm using JUnit and JMockit to create a unit test method that tests the creation and manipulation of a CSV file. How do I intercept the file that is being created to ensure that is created correctly?

@Test
public void testPersistResultsAsCSV() throws IOException {
    final Long id = new Long(1234l);

    TableRow row = new TableRow();
    row.setValue(317l);
    row.setId(1234l);

    final List<TableRow> rows = new ArrayList<TableRow>();
    rows.add(row);

    final List<TableRow> empty = new ArrayList<TableRow>();

    new Expectations() {
        {
            tableService.findTableRowsById(id, (TableQueryOptions)any);
            result = rows;

            tableService.findTableRowsById(id, (TableQueryOptions)any);
            result = empty;

            fileDataService.saveResultsFile((ResultsFile) any);

        }
    };

    resultsToCsvService.persistResultsAsCSV(id);

}