Relax constraints on objects that we'll accept as a file

lib/stripe/file.rb

@@ -20,7 +20,11 @@ def self.create(params = {}, opts = {})
       # rest-client would accept a vanilla `File` for upload, but Faraday does
       # not. Support the old API by wrapping a `File`-like object with an
       # `UploadIO` object if we're given one.
-      if params[:file] && params[:file].respond_to?(:path) && params[:file].respond_to?(:read)
+      if params[:file] && !params[:file].is_a?(String)
+        unless params[:file].respond_to?(:read)
+          raise ArgumentError, "file must respond to `#read`"
+        end
+
         params[:file] = Faraday::UploadIO.new(params[:file], nil)
       end
 

test/stripe/file_test.rb

@@ -61,6 +61,27 @@ class FileTest < Test::Unit::TestCase
         assert_requested :post, "#{Stripe.uploads_base}/v1/files"
         assert file.is_a?(Stripe::File)
       end
+
+      should "be creatable with a string" do
+        file = Stripe::File.create(
+          purpose: "dispute_evidence",
+          file: "my-file-contents",
+          file_link_data: { create: true }
+        )
+        assert_requested :post, "#{Stripe.uploads_base}/v1/files"
+        assert file.is_a?(Stripe::File)
+      end
+
+      should "raise given a file object that doesn't respond to #read" do
+        e = assert_raises(ArgumentError) do
+          Stripe::File.create(
+            purpose: "dispute_evidence",
+            file: Object.new,
+            file_link_data: { create: true }
+          )
+        end
+        assert_equal "file must respond to `#read`", e.message
+      end
     end
 
     should "be deserializable when `object=file`" do