Testpack API support (mars#57)

* Testpack API support including NODE_ENV=test override.

* Hint to the test runner to exit when complete instead of watching.

* 📚 testing and support for Heroku CI

* Format build log

* 📚 minimal `app.json` for CI

Author: mars

README.md

@@ -12,6 +12,8 @@ Deploy React.js web apps generated with [create-react-app](https://github.com/fa
   1. [Create the Heroku app](#user-content-create-the-heroku-app)
   1. [Commit & deploy ♻️](#user-content-commit--deploy-️)
   1. [Continue Development](#user-content-continue-development)
+  1. [Push to Github](#user-content-push-to-github)
+  1. [Testing](#user-content-testing)
 * 👓 [Customization](#user-content-customization)
   * [Procfile](#user-content-procfile)
   * [Web server](#user-content-web-server)
@@ -138,6 +140,25 @@ Then, commit & deploy ♻️
 
 Eventually, to share, collaborate, or simply back-up your code, [create an empty repo at Github](https://github.com/new), and then follow the instructions shown on the repo to **push an existing repository from the command line**.
 
+### Testing
+
+Use [create-react-app's built-in Jest testing](https://github.com/facebookincubator/create-react-app/blob/master/packages/react-scripts/template/README.md#user-content-running-tests) or whatever testing library you prefer. 
+
+As long as tests can be run with `npm test` (like the built-in Jest testing) then it will work effortlessly with [Heroku CI](https://devcenter.heroku.com/articles/heroku-ci).
+
+#### Minimal `app.json`
+
+Heroku CI uses [`app.json`](https://devcenter.heroku.com/articles/app-json-schema) to provision test apps. To enable Heroku CI, commit this minimal example `app.json`:
+
+```json
+{
+  "buildpacks": [
+    {
+      "url": "https://github.com/mars/create-react-app-buildpack"
+    }
+  ]
+}
+```
 
 Customization
 -------------

bin/compile

@@ -31,11 +31,20 @@ branch=""
 dir=$(mktemp -t buildpackXXXXX)
 rm -rf $dir
 
+echo "-----> Configure create-react-app build environment"
 # Set env vars for the inner buildpacks in `.buildpacks`
-# * install build tooling (devDependencies) with npm & Yarn
-# * used only during compile, as the runtime is a static web server
+# * during compile, install build tooling (devDependencies) with npm & Yarn
+# * in runtime, NODE_ENV is not used (this buildpack launches a static web server)
 export NPM_CONFIG_PRODUCTION=false
-export NODE_ENV=development
+INHERITED_NODE_ENV="${NODE_ENV:-development}"
+if [ "$INHERITED_NODE_ENV" = "production" ]
+  then
+  echo '       Setting `NODE_ENV=development` to install dependencies for `npm build`'
+  export NODE_ENV=development
+else
+  echo "       Using \`NODE_ENV=${INHERITED_NODE_ENV}\`"
+  export NODE_ENV="${INHERITED_NODE_ENV}"
+fi
 
 echo "=====> Downloading Buildpack: $url"
 

bin/test

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+# bin/test-compile BUILD_DIR CACHE_DIR ENV_DIR
+
+# Hint to the test runner to exit when complete instead of watching.
+export CI=true
+
+# Test runner copied from Node buildpack:
+# https://github.com/heroku/heroku-buildpack-nodejs/blob/master/bin/test
+
+BUILD_DIR=${1:-}
+if yarn --version > /dev/null 2>&1; then
+  cd "$BUILD_DIR" && yarn test
+else
+  cd "$BUILD_DIR" && npm test
+fi

bin/test-compile

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+# bin/test-compile BUILD_DIR CACHE_DIR ENV_DIR
+
+# Test compiler copied from Node buildpack:
+# https://github.com/heroku/heroku-buildpack-nodejs/blob/master/bin/test-compile
+
+NODE_ENV=test "$(dirname ${0:-})/compile" "$1" "$2" "$3"