Exec should wait for the command to finish before returning

[omertuc]

Describe the bug

Resource.Exec should wait for the command to finish before returning, otherwise the exit code it returns (which it gets from InspectExec) is always 0. Even for an extremely short-running command like false.

To Reproduce

Steps to reproduce the behavior:

package main

import (
	"fmt"
	"os"
	"github.com/ory/dockertest/v3"
)

func main() {
	pool, err := dockertest.NewPool("")
	if err != nil {
		fmt.Println(fmt.Errorf("new pool failed: %v", err.Error()))
		os.Exit(1)
	}

	resource, err := pool.RunWithOptions(&dockertest.RunOptions{
		Repository: "alpine",
		Tag:        "latest",
		Cmd:        []string{"sleep", "10"},
	})

	exitCode, err := resource.Exec([]string{"false"}, dockertest.ExecOptions{})
	if err != nil {
		fmt.Println(fmt.Errorf("exec failed: %v", err.Error()))
		os.Exit(1)
	}

	if exitCode == 0 {
		fmt.Println("This should never happen! yet it does...")
		os.Exit(1)
	}

	return
}

Expected behavior

I expect Exec to only return when the command is finished executing, and I expect the exit code returned by Exec to actually be the exit code of the command that finished and not always 0

Environment

go.sum:

github.com/ory/dockertest/v3 v3.9.1 h1:v4dkG+dlu76goxMiTT2j8zV7s4oPPEppKT8K8p2f1kY=
github.com/ory/dockertest/v3 v3.9.1/go.mod h1:42Ir9hmvaAPm0Mgibk6mBPi7SFvTXxEcnztDYOJ//uM=

docker version

$ docker version
Client:
 Version:           20.10.9
 API version:       1.41
 Go version:        go1.16.8
 Git commit:        c2ea9bc
 Built:             Sun Oct 10 22:41:20 2021
 OS/Arch:           linux/amd64
 Context:           default
 Experimental:      true

Server:
 Engine:
  Version:          20.10.9
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.16.8
  Git commit:       79ea9d3
  Built:            Fri Oct  8 00:00:00 2021
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.5.7
  GitCommit:
 runc:
  Version:          1.0.2
  GitCommit:        c42bf99-dirty
 docker-init:
  Version:          0.19.0
  GitCommit:

/etc/os-release

NAME="Fedora Linux"
VERSION="35 (Workstation Edition)"
ID=fedora
VERSION_ID=35
VERSION_CODENAME=""
PLATFORM_ID="platform:f35"
PRETTY_NAME="Fedora Linux 35 (Workstation Edition)"
ANSI_COLOR="0;38;2;60;110;180"
LOGO=fedora-logo-icon
CPE_NAME="cpe:/o:fedoraproject:fedora:35"
HOME_URL="https://fedoraproject.org/"
DOCUMENTATION_URL="https://docs.fedoraproject.org/en-US/fedora/f35/system-administrators-guide/"
SUPPORT_URL="https://ask.fedoraproject.org/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"
REDHAT_BUGZILLA_PRODUCT="Fedora"
REDHAT_BUGZILLA_PRODUCT_VERSION=35
REDHAT_SUPPORT_PRODUCT="Fedora"
REDHAT_SUPPORT_PRODUCT_VERSION=35
PRIVACY_POLICY_URL="https://fedoraproject.org/wiki/Legal:PrivacyPolicy"
VARIANT="Workstation Edition"
VARIANT_ID=workstation

Additional context

As a workaround users can do something like this, for now, but it's very verbose & awkward:

		exec, err := c.pool.Client.CreateExec(dc.CreateExecOptions{
			Container: c.resource.Container.ID,
			Cmd:       []string{"pg_isready"},
		})
		if err != nil {
			return false, fmt.Errorf("create exec failed: %w", err)
		}

		err = c.pool.Client.StartExec(exec.ID, dc.StartExecOptions{})
		if err != nil {
			return false, fmt.Errorf("start exec failed: %w", err)
		}

		exitCode := -1
		for {
			inspectExec, err := c.pool.Client.InspectExec(exec.ID)
			if err != nil {
				return false, fmt.Errorf("inspect exec failed: %w", err)
			}

			if !inspectExec.Running {
				exitCode = inspectExec.ExitCode
				break
			}
		}

		if exitCode != 0 {
			fmt.Printf("Waiting for docker database. pg_isready err: %v, exit code: %d\n", err, exitCode)
			return false, nil
		}

		return true, nil