How to mock a configfile

Question

I need to test a function which uses CSVHelper

 {
     private readonly CsvConfiguration _csvConfig;

     public CsvWriterService(CsvConfiguration csvConfig)
     {
         _csvConfig = csvConfig;
     }
     public void WriteCsv(TradeRecord record, string filePath)
     {
         using var writer = new StreamWriter(filePath);
         using var csv = new CsvWriter(writer, _csvConfig);

         csv.Context.RegisterClassMap<TradeRecordMap>();
         csv.WriteHeader<TradeRecord>();
         csv.WriteRecord(record);
     }
 }

How can I mock the _csvConfig in the constructor? What I have so far:

private readonly CsvConfiguration _csvConfig;

public CsvWriterServiceTest()
{
    CsvWriterService_Sut = new CsvWriterService(_csvConfig);
}
 [Fact]
 public void WriteCsv_RecordsAndFilePath_Should_WriteCsv()
 {
     //Arrange

     var date = new DateTime(2021, 1, 1);
     var records = new List<TradeRecord>{};
     var filePath = "TestFilePath.csv";

     //Act
     CsvWriterService_Sut.WriteCsv(records, filePath);

     //Assert
     Assert.True(File.Exists(filePath));
 }

CsvWriterService_Sut is not instantiated and gives a NullReferenceException .

Thank you all

Answer 1

Mocking configuration can be a pain and I've found that it's generally not worth mocking it. Personally, I would just create a new instance of CsvConfiguration and pass that into your constructor.

Not everything needs to be mocked in testing. Sometimes you can just use a regular instance of the class.