Added the Golang docker example

Author: keithpitt

Dockerfile

@@ -0,0 +1,6 @@
+FROM golang:cross
+
+# The golang Docker sets the $GOPATH to be /go
+# https://github.com/docker-library/golang/blob/c1baf037d71331eb0b8d4c70cff4c29cf124c5e0/1.4/Dockerfile
+RUN mkdir -p /go/src/github.com/buildkite/golang-docker-example
+WORKDIR /go/src/github.com/buildkite/golang-docker-example

Readme.md

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+# Buildkite Golang Docker Example
+
+This repository is an example on how to test a Golang project through Docker
+using Buildkite.
+
+[Add this example to your Buildkite organization](https://buildkite.com/new)
+
+## Using in your own build pipelines
+
+We've wrapped up the `$GOPATH` wrangling required to get Golang projects to run
+into a `pre-command` hook which you can see here:
+https://github.com/buildkite/golang-example/blob/master/.buildkite/hooks/pre-command
+
+To use in your own build pipelines:
+
+1. Ensure `docker-compose` is installed on your build system. For details on how to do this, see: https://docs.docker.com/compose/install/
+
+2. Use our `Dockerfile` and `docker-compose.yml` files as defaults:
+
+   ```sh
+   cd /your/golang/repo
+   curl -o Dockerfile https://raw.githubusercontent.com/buildkite/golang-golang-example/master/Dockerfile
+   curl -o docker-compose.yml https://raw.githubusercontent.com/buildkite/golang-golang-example/master/docker-compose.yml
+   ```
+
+3. Replace `/go/src/github.com/buildkite/golang-docker-example` in the `Dockerfile` and
+   `docker-compose.yml` files with your own Golang import path.  For example,
+   if your import path in Golang looks like this:
+
+   ```go
+   import (
+     "github.com/keithpitt/project/sub-package"
+   )
+   ```
+
+   Then you would replace `/go/src/github.com/buildkite/golang-docker-example`
+   with `/go/src/github.com/keithpitt/project` (note the `sub-package` part of
+   the import is not included). This path should also match the directory
+   structure within the `$GOPATH` on your own development machine.
+
+4. Add to your build pipeline and add the `BUILDKITE_DOCKER_COMPOSE_CONTAINER` env:
+
+   ```yml
+   steps:
+     - command: "./scripts/test.sh"
+       env:
+         BUILDKITE_DOCKER_COMPOSE_CONTAINER: "app"
+   ```
+
+## License
+
+See [Licence.md](Licence.md) (MIT)

docker-compose.yml

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+app:
+  build: .
+  volumes:
+    - ./:/go/src/github.com/buildkite/golang-docker-example
+    - /usr/bin/buildkite-agent:/usr/bin/buildkite-agent
+  environment:
+    - BUILDKITE_AGENT_ACCESS_TOKEN
+    - BUILDKITE_JOB_ID
+    - BUILDKITE_BUILD_ID
+    - BUILDKITE_BUILD_NUMBER

logger/logger.go

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+package logger
+
+import (
+	"fmt"
+)
+
+func Print(text string) {
+	fmt.Printf("%s", text)
+}

main.go

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+package main
+
+import (
+	"github.com/buildkite/golang-docker-example/logger"
+)
+
+func main() {
+	logger.Print("This is the best Golang program, ever!\n")
+}

main_test.go

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+package main
+
+import (
+	"testing"
+	"github.com/stretchr/testify/assert"
+
+	"os"
+	"io"
+	"bytes"
+)
+
+func TestMain(t *testing.T) {
+	mainStdout := captureStdout(main)
+
+	assert.Equal(t, mainStdout, "This is the best Golang program, ever!\n")
+}
+
+// Source https://gist.github.com/mindscratch/0faa78bd3c0005d080bf
+func captureStdout(f func()) string {
+	old := os.Stdout
+	r, w, _ := os.Pipe()
+	os.Stdout = w
+
+	f()
+
+	w.Close()
+	os.Stdout = old
+
+	var buf bytes.Buffer
+	io.Copy(&buf, r)
+	return buf.String()
+}

scripts/test.sh

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+#!/bin/bash
+
+# Get build + test dependencies. -d also doesn't bother with installing the
+# packages, it just downloads them
+go get -t -d
+go test