Go Code behaves differently in go test vs go run

Question

I'm running go 1.0.3 on my Ubuntu 12.04.1 Laptop and I've stumbled upon a problem where if I run some code in main(), it behaves much more differently than if I run it with go test.

Here's my example:
From main.go

package main

import (
    "image"
    "image/jpeg"
    "fmt"
    "myproj/htmlutil"
    [some imports removed]
)

func main() {
    img, err := htmlutil.GetResizedImageFromWeb("http://img.foodnetwork.com/FOOD/2011/05/04/FNM_060111-OOT-B005_s4x3.jpg")

    if err != nil {
        fmt.Println("There was a problem ",err)
    }
    fmt.Println("Bounds were ",img.Bounds())
}

From myproj/htmlutil_test.go

package htmlutil

import (
    "image"
    "fmt"
    "testing"
    [some imports removed]
)

func TestGetImageFromURL(t *testing.T){
    img, err := GetResizedImageFromWeb("http://img.foodnetwork.com/FOOD/2011/05/04/FNM_060111-OOT-B005_s4x3.jpg")

    if err != nil {
        t.Fatalf("There was a problem %q",err)
    }
    fmt.Println("Bounds were ",img.Bounds())
}

and the function that they call, GetResizedImageFromWeb(), is in myproj/htmlutil.go:

package htmlutil

import (
    "errors"
    "fmt"
    "image"
    "io/ioutil"
    "net/http"
    [some imports removed]
)

func GetResizedImageFromWeb(imageURL string) (image.Image, error) {
    resp, err := http.Get(imageURL)
    if err != nil {
        return nil, errors.New(fmt.Sprint("There was a problem reading the site %q Debug[%s]",imageURL, err))
    }
    defer resp.Body.Close()
    //Decode the image using image's general purpose decoder
    image, s, err := image.Decode(resp.Body)
    if err != nil {
        return nil, err
    }

    return resizeImage(image), nil
}

When I run "go run main.go" from the command line, I see the bounds of the image from the url and can save it as a jpg file on disk if I want using a function in main.go. However, when I run "go test" from the htmlutil package, I get the following error:

There was a problem "image: unknown format"

What is causing the problem to only fail in the unit tests? What am I doing wrong?

My only guess is that for what ever reason, the html.Get() isn't returning all the data in the testing scenario, but I'm still baffled as to why that happens.

Answer 1

In tests you should really check for the results of your function calls.

Tests run with /dev/null on console. Therefore fmt / log outputs are not visible. You should do something like the following in htmlutil_test.go

func TestMain(t *testing.T) {
    img, err := GetResizedImageFromWeb("http://img.foodnetwork.com/FOOD/2011/05/04/FNM_060111-OOT-B005_s4x3.jpg")
    if err != nil {
        t.Error("There was a problem ", err)
    }

    bounds := image.Rectangle{
        image.Point{0, 0},
        image.Point{616, 462}}

    if img.Bounds() != bounds {
        t.Error("Incorrect Bounds were ", img.Bounds())
    }

}

I just copied your code as follows:

main.go

package main

import (
    "errors"
    "fmt"
    "image"
    _ "image/jpeg"
    "net/http"
)

func GetResizedImageFromWeb(imageURL string) (image.Image, error) {
    resp, err := http.Get(imageURL)
    if err != nil {
        return nil, errors.New(fmt.Sprint("There was a problem reading the site %q Debug[%s]", imageURL, err))
    }
    defer resp.Body.Close()
    //Decode the image using image's general purpose decoder
    image, _, err := image.Decode(resp.Body)
    if err != nil {
        return nil, err
    }

    return image, nil
}

func main() {
    img, err := GetResizedImageFromWeb("http://img.foodnetwork.com/FOOD/2011/05/04/FNM_060111-OOT-B005_s4x3.jpg")

    if err != nil {
        fmt.Println("There was a problem ", err)
    }
    fmt.Println("Bounds were ", img.Bounds())
}

main_test.go

package main

import (
    "image"
    "log"
    "testing"
)

func TestMain(t *testing.T) {
    img, err := GetResizedImageFromWeb("http://img.foodnetwork.com/FOOD/2011/05/04/FNM_060111-OOT-B005_s4x3.jpg")
    if err != nil {
        t.Error("There was a problem ", err)
    }

    bounds := image.Rectangle{
        image.Point{0, 0},
        image.Point{616, 462}}

    if img.Bounds() != bounds {
        t.Error("Incorrect Bounds were ", img.Bounds())
    }
}

The output of go test

PASS
ok      test    0.843s

my go version is go version devel +87f67aadaed6 Sat Dec 22 17:41:00 2012 -0800 darwin/amd64