add test for bundle command creation

spec/appraisal/appraisal_spec.rb

@@ -0,0 +1,12 @@
+require 'spec_helper'
+require 'appraisal/appraisal'
+
+describe Appraisal::Appraisal do
+  it "creates a proper bundle command" do
+    appraisal = Appraisal::Appraisal.new('fake', 'fake')
+    appraisal.stub(:gemfile_path)
+      .and_return("/home/test/test directory")
+
+    appraisal.bundle_command.should == "bundle install --gemfile='/home/test/test directory'"
+  end
+end