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: container_start_test.go
    path of file: ./repos/moby/client
    
    the code of the file until where you have to start completion: package client // import "github.com/docker/docker/client"

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"testing"

	"github.com/docker/docker/api/types/container"
	"github.com/docker/docker/errdefs"
	"gotest.tools/v3/assert"
	is "gotest.tools/v3/assert/cmp"
)

func TestContainerStartError(t *testing.T) {
	client := &Client{
		client: newMockClient(errorMock(http.StatusInternalServerError, "Server error")),
	}
	err := client.ContainerStart(context.Background(), "nothing", container.StartOptions{})
	assert.Check(t, is.ErrorType(err, errdefs.IsSystem))
}

func TestContainerStart(t *testing.T) {
	expectedURL := "/containers/container_id/start"
	client := &Client{
		client: newMockClient(func(req *http.Request) (*http.Response, error) {
			if !strings.HasPrefix(req.URL.Path, expectedURL) {
				return nil, fmt.Errorf("Expected URL '%s', got '%s'", expectedURL, req.URL)
			}
			// we're not expecting any payload, but if one is supplied, check it 
    
func TestContainerStart(t *testing.T) {
	expectedURL := "/containers/container_id/start"
	client := &Client{
		client: newMockClient(func(req *http.Request) (*http.Response, error) {
			if !strings.HasPrefix(req.URL.Path, expectedURL) {
				return nil, fmt.Errorf("Expected URL '%s', got '%s'", expectedURL, req.URL)
			}
			// we're not expecting any payload, but if one is supplied, check it is valid.
			if req.Header.Get("Content-Type") == "application/json" {
				var startConfig interface{}
				if err := json.NewDecoder(req.Body).Decode(&startConfig); err != nil {
					return nil, fmt.Errorf("Unable to parse json: %s", err)
				}
			}

			checkpoint := req.URL.Query().Get("checkpoint")
			if checkpoint != "checkpoint_id" {
				return nil, fmt.Errorf("checkpoint not set in URL query properly. Expected 'checkpoint_id', got %s", checkpoint)
			}

			return &http.Response{
				StatusCode: http.StatusOK,
				Body:       io.NopCloser(bytes.NewReader([]byte(""))),
			}, nil
		}),
	}

	err := client.ContainerStart(context.Background(), "container_id", container.StartOptions{CheckpointID: "checkpoint_id"})
	if err != nil {
		t.Fatal(err)
	}
}