表驱动的文件创建测试

I got an example from @volker about table driven test like following But currently I miss what I should put in the real test, this test is using byte, currently im not sure what to put in the args and the expected []byte, e.g. I want to check that in the file there is 2 new line and then application entry, how can I do it without the need to create the real file and parse it?

type Models struct {
    name        string
    vtype       string
    contentType string
}

func setFile(file io.Writer, appStr Models) {
    fmt.Fprint(file, "1.0")

    fmt.Fprint(file, "Created-By: application generation process")
    for _, mod := range appStr.Modules {
        fmt.Fprint(file, "
")
        fmt.Fprint(file, "
")
        fmt.Fprint(file,  appStr.vtype) //"userApp"
        fmt.Fprint(file, "
")
        fmt.Fprint(file, appStr.name) //"applicationValue"
        fmt.Fprint(file, "
")
        fmt.Fprint(file, appStr.contentType)//"ContentType"
    }
}

func Test_setFile(t *testing.T) {
    type args struct {
        appStr models.App
    }
    var tests []struct {
        name string
        args args
        expected []byte
   }
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            b := &bytes.Buffer{}
            setFile(b, tt.args.AppStr)
            if !bytes.Equal(b.Bytes(), tt.expected) {
                t.Error("somewhat bad happen")
            }
        })
    }
}

I read and understand the following example but not for byte and file https://medium.com/@virup/how-to-write-concise-tests-table-driven-tests-ed672c502ae4

If you are only checking for the static content at the beginning, then you really only need one test. It would look something like this:

func Test_setFile(t *testing.T) {
    type args struct {
        appStr models.App
    }
    var tests []struct {
        name string
        args args
        expected []byte
    }{
        name: 'Test Static Content',
        args: args{appStr: 'Some String'},
        expected: []byte(fmt.Sprintf("%s%s%s", NEW_LINE, NEW_LINE, "Application")),
    }
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            b := &bytes.Buffer{}
            setFile(b, tt.args.AppStr)
            if !bytes.Equal(b.Bytes(), tt.expected) {
                t.Error("somewhat bad happen")
            }
        })
    }
}

Although, since you only have one case for this test, there really isn't a need to use table driven tests here. You could clean it up to look something like this:

func Test_setFile(t *testing.T) {
    b := &bytes.Buffer{}
    setFile(b, 'Some String')
    want := []byte(fmt.Sprintf("%s%s%s", NEW_LINE, NEW_LINE, "Application"))
    got := b.Bytes()
    if !bytes.Equal(want, got) {
        t.Errorf("want: %s got: %s", want, got)
    }
}