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: downloader_s3_test.go
    path of file: ./repos/juju/api/client/charms
    
    the code of the file until where you have to start completion: // Copyright 2023 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package charms_test

import (
	"net/url"

	"github.com/juju/names/v5"
	"go.uber.org/mock/gomock"
	gc "gopkg.in/check.v1"

	basemocks "github.com/juju/juju/api/base/mocks"
	"github.com/juju/juju/api/client/charms"
	"github.com/juju/juju/downloader"
)

type charmS3DownloaderSuite struct {
}

var _ = gc.Suite(&charmS3DownloaderSuite{})

func (s *charmS3DownloaderSuite) TestCharmOpener(c *gc.C) {
	correctURL, err := url.Parse("ch:mycharm")
	c.Assert(err, gc.IsNil)

	tests := []struct {
		name               string
		req                downloader.Request
		mocks              func(*MockCharmGetter, *basemocks.MockAPICaller)
		expectedErrPattern string
	}{
		{
			name: "invalid ArchiveSha256 in request
    
func (s *charmS3DownloaderSuite) TestCharmOpener(c *gc.C) {
	correctURL, err := url.Parse("ch:mycharm")
	c.Assert(err, gc.IsNil)

	tests := []struct {
		name               string
		req                downloader.Request
		mocks              func(*MockCharmGetter, *basemocks.MockAPICaller)
		expectedErrPattern string
	}{
		{
			name: "invalid ArchiveSha256 in request",
			req: downloader.Request{
				ArchiveSha256: "abcd012",
			},
			expectedErrPattern: "download request with archiveSha256 length 7 not valid",
		},
		{
			name: "invalid URL in request",
			req: downloader.Request{
				ArchiveSha256: "abcd0123",
				URL: &url.URL{
					Scheme: "badscheme",
					Host:   "badhost",
				},
			},
			expectedErrPattern: "did not receive a valid charm URL.*",
		},
		{
			name: "open charm OK",
			req: downloader.Request{
				ArchiveSha256: "abcd0123",
				URL:           correctURL,
			},
			mocks: func(mockGetter *MockCharmGetter, mockCaller *basemocks.MockAPICaller) {

				modelTag := names.NewModelTag("testmodel")
				mockCaller.EXPECT().ModelTag().Return(modelTag, true)
				mockGetter.EXPECT().GetCharm(gomock.Any(), "testmodel", "mycharm-abcd0123").MinTimes(1).Return(nil, nil)
			},
		},
	}

	for i, tt := range tests {
		c.Logf("test %d - %s", i, tt.name)

		ctrl := gomock.NewController(c)
		defer ctrl.Finish()

		mockCaller := basemocks.NewMockAPICaller(ctrl)
		mockGetter := NewMockCharmGetter(ctrl)
		if tt.mocks != nil {
			tt.mocks(mockGetter, mockCaller)
		}

		charmOpener := charms.NewS3CharmOpener(mockGetter, mockCaller)
		r, err := charmOpener.OpenCharm(tt.req)

		if tt.expectedErrPattern != "" {
			c.Assert(r, gc.IsNil)
			c.Assert(err, gc.ErrorMatches, tt.expectedErrPattern)
		} else {
			c.Assert(err, gc.IsNil)
		}
	}
}