Go: Testing Against Application Binaries

Unit-testing in Go is simple and a pleasure. The minimum structure required to do unit-tests is scarcely more than that required to write any kind of code. In fact, most of the time it is so easy that you are almost, arguably, guaranteed to waste time doing any debugging at all before you have written unit-tests.

However, it may take a little more thought to test your executables. Even though you can still have a unit-testing source-file (“*_test.go”) and you can call your main() to do something, it’s non-trivial to capture your output and/or pass arguments:

  • You might end-up using os.Pipe() to hook stdout/stderr and launching a goroutine to read from the other end, but you might have issues.
  • Your test might call back into the execute in os.Args[0] (the tests run from a test-specific binary generated by the testing process), but this won’t accept the arbitrary command-line arguments required by your application.
  • You might wrap a call to “go test” and try to pass “-args ” (“-args” is like “–” for tests, where all following arguments are passed verbatim), but I have had issues with this.

Naturally, you want to avoid having to kick-off a build of your application at the top of the tests in order to have something to test against.

You can use “go run” with exec.Command (in os/exec) to easily accomplish all of this while still avoiding a manual build. You can even provide it alternative io.Writer instances in order to capture stdout/stderr output.


package main

import (


var (
    assetsPath = ""
    appFilepath = ""

func TestMain(t *testing.T) {
    imageFilepath := path.Join(assetsPath, "NDM_8901.jpg")

    cmd := exec.Command(
            "go", "run", appFilepath,
            "-filepath", imageFilepath)

    b := new(bytes.Buffer)
    cmd.Stdout = b
    cmd.Stderr = b

    err := cmd.Run()
    actual := b.String()

    if err != nil {

    expected := `IFD=[IfdIdentity] ID=(0x010f) NAME=[Make] COUNT=(6) TYPE=[ASCII] VALUE=[Canon]
IFD=[IfdIdentity] ID=(0x0110) NAME=[Model] COUNT=(22) TYPE=[ASCII] VALUE=[Canon EOS 5D Mark III]
IFD=[IfdIdentity] ID=(0x0112) NAME=[Orientation] COUNT=(1) TYPE=[SHORT] VALUE=[1]
IFD=[IfdIdentity] ID=(0x011a) NAME=[XResolution] COUNT=(1) TYPE=[RATIONAL] VALUE=[72/1]
IFD=[IfdIdentity] ID=(0x011b) NAME=[YResolution] COUNT=(1) TYPE=[RATIONAL] VALUE=[72/1]
IFD=[IfdIdentity] ID=(0x0128) NAME=[ResolutionUnit] COUNT=(1) TYPE=[SHORT] VALUE=[2]
IFD=[IfdIdentity] ID=(0x0128) NAME=[ResolutionUnit] COUNT=(1) TYPE=[SHORT] VALUE=[2]
IFD=[IfdIdentity] ID=(0x0201) NAME=[JPEGInterchangeFormat] COUNT=(1) TYPE=[LONG] VALUE=[11444]
IFD=[IfdIdentity] ID=(0x0202) NAME=[JPEGInterchangeFormatLength] COUNT=(1) TYPE=[LONG] VALUE=[21491]

    if actual != expected {
        t.Fatalf("Output not as expected:\n%s", actual)

func init() {
    goPath := os.Getenv("GOPATH")

    assetsPath = path.Join(goPath, "src", "github.com", "dsoprea", "go-exif", "assets")
    appFilepath = path.Join(goPath, "src", "github.com", "dsoprea", "go-exif", "exif-read-tool", "main.go")

Spawn an SSL Webserver in Your Python Unit-Tests

You might eventually have to unit-test a website that has a functional need to be run as SSL. For example, you might need to test a client that must connect using SSL authentication.

You can accomplish this by combining Python’s built-in webserver with ssl.SSLSocket.

This code is a distant relative of another example, but is lighter, simpler, and more Pythonic.

It runs out of the current directory (you’ll have to chdir() from the code if you want something different, since the webserver doesn’t take a path), and expects server.private_key.pem and server.crt.pem to exist.

import os.path
import socket
import SocketServer
import BaseHTTPServer
import SimpleHTTPServer
import ssl

class _SecureHTTPRequestHandler(SimpleHTTPServer.SimpleHTTPRequestHandler):
    def setup(self):
        self.connection = self.request
        self.rfile = socket._fileobject(self.request, 'rb', self.rbufsize)
        self.wfile = socket._fileobject(self.request, 'wb', self.wbufsize)

class _SecureHTTPServer(BaseHTTPServer.HTTPServer):
    def __init__(self, private_key_pem_filepath, cert_pem_filepath,
                 binding=None, handler_cls=_SecureHTTPRequestHandler):
        if binding is None:
            # The default port is 1443 so that we don't have to be root.
            binding = ('', 1443)

        # We can't use super() because it's not a new-style class.
        SocketServer.BaseServer.__init__(self, binding, handler_cls)

        s = socket.socket(self.address_family, self.socket_type)
        self.socket = ssl.SSLSocket(


app_path = os.path.abspath(os.path.dirname(__file__))

private_key_pem_filepath = os.path.join(app_path, 'server.private_key.pem')
certificate_pem_filepath = os.path.join(app_path, 'server.crt.pem')

httpd = _SecureHTTPServer(


This code may also be found in the RandomUtility repository.