[Fact]
public void A_new_file_is_created_when_the_current_file_overflows()
{
    var sut = new AuditManager(3);
    var files = new FileContent[]
    {
        new FileContent("audit_1".txt, new String[0]),
        new FileContent("audit_2".txt, new String[]
        {
            "Peter; 2019-04-06T16:30:00",
            "Jane; 2019-04-06T16:40:00",
            "Jack; 2019-04-06T17:00:00"
        })
    };
    
    FileUpdate update = sut.AddRecord(
        files, "Alice", DateTime.parse("2019-04-06T18:00:00"));
    
    Assert.Equal("audit_3.txt", update.FileName);
    Assert.Equal("Alice;2019-04-06T18:00:00", update.NewContent);
}