add tests for UploadIO#from_io

spec/google/apis/core/upload_spec.rb

@@ -22,6 +22,7 @@ require 'hurley/test'
 # TODO: Upload from file
 
 RSpec.describe Google::Apis::Core::UploadIO do
+  context 'from_file' do
     let(:upload_io) { Google::Apis::Core::UploadIO.from_file(file) }
 
     context 'with text file' do
@@ -49,6 +50,25 @@ RSpec.describe Google::Apis::Core::UploadIO do
     end
   end
 
+  context 'from_io' do
+
+    context 'with i/o stream' do
+      let(:io) { StringIO.new 'Hello google' }
+      
+      it 'should setup default content-type' do
+        upload_io = Google::Apis::Core::UploadIO.from_io(io)  
+        expect(upload_io.content_type).to eql Google::Apis::Core::UploadIO::OCTET_STREAM_CONTENT_TYPE
+      end
+
+      it 'should allow overring the mime type' do
+        upload_io = Google::Apis::Core::UploadIO.from_io(io, content_type: 'application/x-gzip')
+        expect(upload_io.content_type).to eq('application/x-gzip')
+      end
+    end
+
+  end
+end
+
 RSpec.describe Google::Apis::Core::RawUploadCommand do
   include TestHelpers
   include_context 'HTTP client'