打开和读取文件的单元测试功能

Question

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!

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
}

Answer 1

You need to refactor your code and make more suitable for testing.

Here is how I would do it:

func openAndReadFile(fileName string) [][]string {
    file, err := os.Open(fileName)
    if err != nil {
        fmt.Printf("Failed to open file: %s", fileName)
    }
    lines, err := readFile(file)
    if err != nil {
        fmt.Printf("Failed to read file: %s", fileName)
    }
    return lines
}

func readFile(reader io.Reader) ([][]string, error) {
    r := csv.NewReader(reader)
    lines, err := r.ReadAll()
    if err != nil {
        log.Fatal(err)
    }
    return lines, err
}

Then for testing you can simply use any data structure that implements the io.reader interface. For example, I use a bytes buffer, but you can choose a network connection:

func TestReadFile(t *testing.T) {
    var buffer bytes.Buffer
    buffer.WriteString("fake, csv, data")
    content, err := readFile(&buffer)
    if err != nil {
        t.Error("Failed to read csv data")
    }
    fmt.Print(content)
}