Test that adding an invalid box results in an error

test/acceptance/box_test.rb

@@ -20,14 +20,25 @@ class BoxTest < AcceptanceTest
     assert(results.stdout.read =~ /^foo$/, "Box should exist after it is added")
   end
 
-  should "give a helpful error message if the file doesn't exist" do
-    # Add a box which doesn't exist
+  should "give an error if the file doesn't exist" do
     results = execute("vagrant", "box", "add", "foo", "/tmp/nope/nope/nope/nonono.box")
     assert(!results.success?, "Box add should fail.")
     assert(results.stdout.read =~ /^The specified path to a file doesn't exist.$/,
            "This should show an error message about the file not existing.")
   end
 
+  should "give an error if the file is not a valid box" do
+    invalid = @environment.workdir.join("nope.txt")
+    invalid.open("w+") do |f|
+      f.write("INVALID!")
+    end
+
+    results = execute("vagrant", "box", "add", "foo", invalid.to_s)
+    assert(!results.success?, "Box add should fail.")
+    assert(results.stdout.read =~ /^The box file you're attempting to add is invalid./,
+           "should show an error message")
+  end
+
   should "add a box from an HTTP server" do
     # TODO: Spin up an HTTP server to serve a file, add and test.
     skip("Need to setup HTTP server functionality")