module ActionDispatch::TestProcess::FixtureFile

def file_fixture_upload(path, mime_type = nil, binary = false)

post :change_avatar, params: { avatar: file_fixture_upload('david.png', 'image/png', :binary) }

will not affect other platforms:
To upload binary files on Windows, pass `:binary` as the last parameter. This

Default fixture files location is `test/fixtures/files`.

post :change_avatar, params: { avatar: file_fixture_upload('david.png', 'image/png') }

`Rack::Test::UploadedFile.new(File.join(ActionDispatch::IntegrationTest.file_fixture_path, path), type)`:
Shortcut for 
def file_fixture_upload(path, mime_type = nil, binary = false)
  if self.class.file_fixture_path && !File.exist?(path)
    path = file_fixture(path)
  end
  Rack::Test::UploadedFile.new(path, mime_type, binary)
end