You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: simplestreams_test.go
    path of file: ./repos/juju/environs/imagedownloads
    
    the code of the file until where you have to start completion: // Copyright 2016 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package imagedownloads_test

import (
	"fmt"
	"io"
	"net/http"
	"net/http/httptest"
	"strings"

	"github.com/juju/testing"
	jc "github.com/juju/testing/checkers"
	"golang.org/x/crypto/openpgp"
	openpgperrors "golang.org/x/crypto/openpgp/errors"
	gc "gopkg.in/check.v1"

	corebase "github.com/juju/juju/core/base"
	. "github.com/juju/juju/environs/imagedownloads"
	"github.com/juju/juju/environs/imagemetadata"
	"github.com/juju/juju/environs/simplestreams"
	streamstesting "github.com/juju/juju/environs/simplestreams/testing"
)

type Suite struct {
	tes
    
func (*Suite) TestFetchManyDefaultFilterAndCustomImageDownloadURL(c *gc.C) {
	ss := simplestreams.NewSimpleStreams(streamstesting.TestDataSourceFactory())
	ts := httptest.NewServer(&sstreamsHandler{})
	defer ts.Close()
	tds := []simplestreams.DataSource{
		newTestDataSource(ss, ts.URL)}
	constraints, err := imagemetadata.NewImageConstraint(
		simplestreams.LookupParams{
			Arches:   []string{"amd64", "arm64", "ppc64el"},
			Releases: []string{"16.04"},
			Stream:   "released",
		},
	)
	c.Assert(err, jc.ErrorIsNil)
	got, resolveInfo, err := Fetch(ss, tds, constraints, nil)
	c.Check(resolveInfo.Signed, jc.IsTrue)
	c.Check(err, jc.ErrorIsNil)
	c.Assert(len(got), jc.DeepEquals, 27)
	for _, v := range got {
		// Note: instead of the index URL, we are pulling the actual
		// images from a different operator-provided URL.
		gotURL, err := v.DownloadURL("https://tasty-cloud-images.ubuntu.com")
		c.Check(err, jc.ErrorIsNil)
		c.Check(strings.HasPrefix(gotURL.String(), "https://tasty-cloud-images.ubuntu.com"), jc.IsTrue, gc.Commentf("expected image download URL to use the operator-provided URL"))
		c.Check(strings.HasSuffix(gotURL.String(), v.FType), jc.IsTrue)
		c.Check(strings.Contains(gotURL.String(), v.Release), jc.IsTrue)
		c.Check(strings.Contains(gotURL.String(), v.Version), jc.IsTrue)
	}
}