In order to keep the effort to 'interfaces to your filesystem operations and "mock them out"' as @Doc Brown answer suggested as small as possible it is a good idea to use java binary streams or text reader (or ther equivalent in c# or the programming language you are using) instead of using Files with filenames directly in you tdd-developed class.

Example:

Using java I have implemented a class CsvReader

public class CsvReader {
    private Reader reader;

    public CsvReader(Reader reader) {
        this.reader = reader;
    }
}

For testing I used in memory data like this

String contentOfCsv = "TestColumn1;TestColumn2\n"+
    "value1;value2\n";

CsvReader sut = new CsvReader(java.io.StringReader(contentOfCsv));

or embend testdata into the resources

CsvReader sut = new CsvReader(getClass().getResourceAsStream("/data.csv"));

In production I use the file system

CsvReader sut = new CsvReader(new BufferedReader( new FileReader( "/import/Prices.csv" ) ));

I understand your question as "A good/accepted way to test a class that depends on file system operations". I donot assume that you want to test the filesystem of your os.

In order to keep the effort to 'interfaces to your filesystem operations and "mock them out"' as @Doc Brown answer suggested as small as possible it is a good idea to use java binary streams or text reader (or ther equivalent in c# or the programming language you are using) instead of using Files with filenames directly in you tdd-developed class.

Example:

Using java I have implemented a class CsvReader

public class CsvReader {
    private Reader reader;

    public CsvReader(Reader reader) {
        this.reader = reader;
    }
}

For testing I used in memory data like this

String contentOfCsv = "TestColumn1;TestColumn2\n"+
    "value1;value2\n";

CsvReader sut = new CsvReader(java.io.StringReader(contentOfCsv));

or embend testdata into the resources

CsvReader sut = new CsvReader(getClass().getResourceAsStream("/data.csv"));

In production I use the file system

CsvReader sut = new CsvReader(new BufferedReader( new FileReader( "/import/Prices.csv" ) ));

This way my CsvReader does not depend on filesystem but on an abstraction "Reader" where there is an implementation for filesystem.

In order to keep the effort to 'interfaces to your filesystem operations and "mock them out"' as @Doc Brown answer suggested as small as possible it is a good idea to use java binary streams or text reader (or ther equivalent in c# or the programming language you are using).

Example:

Using java I have implemented a class CsvReader

public class CsvReader {
    private Reader reader;

    public CsvReader(Reader reader) {
        this.reader = reader;
    }
}

For testing I used in memory data like this

String contentOfCsv = "TestColumn1;TestColumn2\n"+
    "value1;value2\n";

CsvReader sut = new CsvReader(java.io.StringReader(contentOfCsv));

or embend testdata into the resources

CsvReader sut = new CsvReader(getClass().getResourceAsStream("/data.csv"));

In production I use the file system

CsvReader sut = new CsvReader(new BufferedReader( new FileReader( "/import/Prices.csv" ) ));

In order to keep the effort to 'interfaces to your filesystem operations and "mock them out"' as @Doc Brown answer suggested as small as possible it is a good idea to use java binary streams or text reader (or ther equivalent in c# or the programming language you are using) instead of using Files with filenames directly in you tdd-developed class.

Example:

Using java I have implemented a class CsvReader

public class CsvReader {
    private Reader reader;

    public CsvReader(Reader reader) {
        this.reader = reader;
    }
}

For testing I used in memory data like this

String contentOfCsv = "TestColumn1;TestColumn2\n"+
    "value1;value2\n";

CsvReader sut = new CsvReader(java.io.StringReader(contentOfCsv));

or embend testdata into the resources

CsvReader sut = new CsvReader(getClass().getResourceAsStream("/data.csv"));

In production I use the file system

CsvReader sut = new CsvReader(new BufferedReader( new FileReader( "/import/Prices.csv" ) ));