module ActionDispatch::TestProcess::FixtureFile

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

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

Default fixture files location is test/fixtures/files.

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

Shortcut for Rack::Test::UploadedFile.new(File.join(ActionDispatch::IntegrationTest.file_fixture_path, path), type):

def fixture_file_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