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: collection_group_test.go
    path of file: ./repos/golang-samples/firestore
    
    the code of the file until where you have to start completion: // Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package firestore

import (
	"bytes"
	"context"
	"os"
	"strings"
	"testing"

	"cloud.google.com/go/firestore"
	"github.com/GoogleCloudPlatform/golang-samples/internal/testutil"
)

func TestCollectionGroup(t *testing.T) {
	tc := testutil.SystemTest(t)
	/
    
func TestCollectionGroupPartitionQueries(t *testing.T) {
	tc := testutil.SystemTest(t)
	// TODO(#559): revert this to testutil.SystemTest(t).ProjectID
	// when datastore and firestore can co-exist in a project.
	projectID := os.Getenv("GOLANG_SAMPLES_FIRESTORE_PROJECT")
	if projectID == "" {
		t.Skip("Skipping firestore test. Set GOLANG_SAMPLES_FIRESTORE_PROJECT.")
	}

	ctx := context.Background()

	client, err := firestore.NewClient(ctx, projectID)
	if err != nil {
		t.Fatalf("firestore.NewClient: %v", err)
	}
	defer client.Close()

	collection := tc.ProjectID + "-collection-group-cities"

	// Delete all docs first to make sure collectionGroupSetup works.
	docs, err := client.Collection(collection).DocumentRefs(ctx).GetAll()
	// Ignore errors; this isn't essential.
	if err == nil {
		for _, d := range docs {
			d.Delete(ctx)
		}
	}

	if err := collectionGroupSetup(projectID, collection); err != nil {
		t.Fatalf("collectionGroupSetup: %v", err)
	}

	err = partitionQuery(ctx, client)
	if err != nil {
		t.Errorf("partitionQuery unexpected result: %s", err)
	}

	err = serializePartitionQuery(ctx, client)
	if err != nil {
		t.Errorf("serializePartitionQuery unexpected result: %s", err)
	}
}