support for injecting env during testing

spec/simple_spec.rb

@@ -14,9 +14,10 @@ RSpec.describe "Simple" do
     app.destroy
   end
 
-  let(:app)  { AppRunner.new(name, @debug) }
+  let(:app)  { AppRunner.new(name, env, @debug) }
 
   let(:name) { "hello_world" }
+  let(:env)  { Hash.new }
 
   it "should serve out of public_html by default" do
     response = app.get("/")

spec/support/app_runner.rb

@@ -19,11 +19,13 @@ class AppRunner
   HOST_IP        = boot2docker_ip || "127.0.0.1"
   CONTAINER_PORT = "3000"
 
-  def initialize(fixture, debug = false)
+  def initialize(fixture, env = nil, debug = false)
     @debug     = debug
     @container = Docker::Container.create(
       'Image'      => BuildpackBuilder::TAG,
       'Cmd'        => ["bash", "-c", "cp -rf /src/* /app/ && /app/bin/boot"],
+      # Env format is [KEY1=VAL1 KEY2=VAL2]
+      'Env'        => env.to_a.map {|i| i.join("=") },
       'HostConfig' => {
         'Binds' => ["#{fixtures_path(fixture)}:/src"],
         'PortBindings' => {