core: add test for fs_real_path on Windows

test/unit/base.rb

@@ -30,6 +30,8 @@ RSpec.configure do |c|
 
   if Vagrant::Util::Platform.windows?
     c.filter_run_excluding :skip_windows
+  else
+    c.filter_run_excluding :windows
   end
 end
 

test/unit/vagrant/util/platform_test.rb

@@ -0,0 +1,13 @@
+require File.expand_path("../../../base", __FILE__)
+
+require "vagrant/util/platform"
+
+describe Vagrant::Util::Platform do
+  subject { described_class }
+
+  describe "#fs_real_path" do
+    it "fixes drive letters on Windows", :windows do
+      expect(described_class.fs_real_path("c:/foo").to_s).to eql("C:/foo")
+    end
+  end
+end