builder/docker: StepPull test, driver abstraction for tests

builder/docker/builder.go

@@ -56,6 +56,11 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 	state.Put("hook", hook)
 	state.Put("ui", ui)
 
+	// Setup the driver that will talk to Docker
+	state.Put("driver", &DockerDriver{
+		Ui: ui,
+	})
+
 	// Run!
 	if b.config.PackerDebug {
 		b.runner = &multistep.DebugRunner{

builder/docker/driver.go

@@ -0,0 +1,9 @@
+package docker
+
+// Driver is the interface that has to be implemented to communicate with
+// Docker. The Driver interface also allows the steps to be tested since
+// a mock driver can be shimmed in.
+type Driver interface {
+	// Pull should pull down the given image.
+	Pull(image string) error
+}

builder/docker/driver_docker.go

@@ -0,0 +1,15 @@
+package docker
+
+import (
+	"github.com/mitchellh/packer/packer"
+	"os/exec"
+)
+
+type DockerDriver struct {
+	Ui packer.Ui
+}
+
+func (d *DockerDriver) Pull(image string) error {
+	cmd := exec.Command("docker", "pull", image)
+	return runAndStream(cmd, d.Ui)
+}

builder/docker/driver_mock.go

@@ -0,0 +1,15 @@
+package docker
+
+// MockDriver is a driver implementation that can be used for tests.
+type MockDriver struct {
+	PullError error
+
+	PullCalled bool
+	PullImage  string
+}
+
+func (d *MockDriver) Pull(image string) error {
+	d.PullCalled = true
+	d.PullImage = image
+	return d.PullError
+}

builder/docker/step_pull.go

@@ -4,18 +4,17 @@ import (
 	"fmt"
 	"github.com/mitchellh/multistep"
 	"github.com/mitchellh/packer/packer"
-	"os/exec"
 )
 
 type StepPull struct{}
 
 func (s *StepPull) Run(state multistep.StateBag) multistep.StepAction {
 	config := state.Get("config").(*Config)
+	driver := state.Get("driver").(Driver)
 	ui := state.Get("ui").(packer.Ui)
 
 	ui.Say(fmt.Sprintf("Pulling Docker image: %s", config.Image))
-	cmd := exec.Command("docker", "pull", config.Image)
+	if err := driver.Pull(config.Image); err != nil {
-	if err := runAndStream(cmd, ui); err != nil {
 		err := fmt.Errorf("Error pulling Docker image: %s", err)
 		state.Put("error", err)
 		ui.Error(err.Error())

builder/docker/step_pull_test.go

@@ -0,0 +1,52 @@
+package docker
+
+import (
+	"errors"
+	"github.com/mitchellh/multistep"
+	"testing"
+)
+
+func TestStepPull_impl(t *testing.T) {
+	var _ multistep.Step = new(StepPull)
+}
+
+func TestStepPull(t *testing.T) {
+	state := testState(t)
+	step := new(StepPull)
+	defer step.Cleanup(state)
+
+	config := state.Get("config").(*Config)
+	driver := state.Get("driver").(*MockDriver)
+
+	// run the step
+	if action := step.Run(state); action != multistep.ActionContinue {
+		t.Fatalf("bad action: %#v", action)
+	}
+
+	// verify we did the right thing
+	if !driver.PullCalled {
+		t.Fatal("should've pulled")
+	}
+	if driver.PullImage != config.Image {
+		t.Fatalf("bad: %#v", driver.PullImage)
+	}
+}
+
+func TestStepPull_error(t *testing.T) {
+	state := testState(t)
+	step := new(StepPull)
+	defer step.Cleanup(state)
+
+	driver := state.Get("driver").(*MockDriver)
+	driver.PullError = errors.New("foo")
+
+	// run the step
+	if action := step.Run(state); action != multistep.ActionHalt {
+		t.Fatalf("bad action: %#v", action)
+	}
+
+	// verify we have an error
+	if _, ok := state.GetOk("error"); !ok {
+		t.Fatal("should have error")
+	}
+}

builder/docker/step_test.go

@@ -10,6 +10,7 @@ import (
 func testState(t *testing.T) multistep.StateBag {
 	state := new(multistep.BasicStateBag)
 	state.Put("config", testConfigStruct(t))
+	state.Put("driver", &MockDriver{})
 	state.Put("hook", &packer.MockHook{})
 	state.Put("ui", &packer.BasicUi{
 		Reader: new(bytes.Buffer),