title: Unit test function that is opening and reading a file
body: <p>I am working on learning go with a simple program that is doing some file reading and am working on adding unit testing to my program. I have ran into an issue/question while doing this. I want to unit test the function below and my question is that the function takes a name of the file which is then opened and processed. During testing I do not want to actually pass it a real file. I am wondering is this something I can somehow mock so that I can just pass it a "fake" file and have it process that instead? Thanks!    </p>
  
  <pre><code>func openAndReadFile(fileName string) [][]string {
      file, err := os.Open(fileName)
      if err != nil {
          fmt.Printf("Failed to read file: %s", fileName)
      }
      r := csv.NewReader(file)
      lines, err := r.ReadAll()
      if err != nil {
          log.Fatal(err)
      }
      return lines
  }
  </code></pre>