CODEWITHSUNDEEP
unit-testinggo
jsm1th
jsm1th

Reputation: 489

Unit test function that is opening and reading a file

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
}

Upvotes: 14

Views: 21444

Answers (3)

Sudhir Jonathan
Sudhir Jonathan

Reputation: 17516

I'd strongly suggest using an interface instead of the filename string like the other answers here are recommending, but if you really must do this the only way is likely with a temp file. The decision to use a string file name has locked the code into assuming something to be present on the file system and has pushed in the responsibility of file management.

Upvotes: 0

Dirk Herrmann
Dirk Herrmann

Reputation: 5939

The function you have shown is dominated by interactions: Interactions with the file system and interactions with the csv reader. To be sure that these interactions work nicely you will later anyway have to do some integration-testing against the file system and the csv reader. Think about which bugs you are hoping to find, and you will see that bugs are more likely on the interaction level: Is the order of file,err correct, or should it be the other way around? Is nil really the value indicating no error? Do you have to give more arguments to Open? etc.

Therefore, I would not concentrate on unit-testing this function. However, this function is a good candidate to be mocked to make unit-testing the surrounding code easier. Thus, mock openAndReadFile to unit-test the surrounding code, and test openAndReadFile using integration-testing.

Upvotes: 4

georgeok
georgeok

Reputation: 5706

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)
}

Upvotes: 23

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