Implement typed error for docker runner: ErrNoImage (#3123)

* Implement typed error for docker runner (ErrNoImage)

* remove logs

Author: intojhanurag

pkg/docker/runner.go

@@ -33,6 +33,12 @@ const (
 	DefaultStopTimeout = 10 * time.Second
 )
 
+type ErrNoImage struct{}
+
+func (e ErrNoImage) Error() string {
+	return "Function has no associated image. Has it been built?"
+}
+
 // Runner starts and stops functions as local containers.
 type Runner struct {
 	verbose bool // Verbose logging
@@ -81,7 +87,7 @@ func (n *Runner) Run(ctx context.Context, f fn.Function, address string, startTi
 	port = choosePort(host, port, DefaultDialTimeout)
 
 	if f.Build.Image == "" {
-		return job, errors.New("Function has no associated image. Has it been built?")
+		return job, ErrNoImage{}
 	}
 	if c, _, err = NewClient(client.DefaultDockerHost); err != nil {
 		return job, errors.Wrap(err, "failed to create Docker API client")

pkg/docker/runner_test.go

@@ -2,6 +2,7 @@ package docker_test
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -48,9 +49,8 @@ func TestDockerRunImagelessError(t *testing.T) {
 	f := fn.NewFunctionWith(fn.Function{})
 
 	_, err := runner.Run(context.Background(), f, "", fn.DefaultStartTimeout)
-	// TODO: switch to typed error:
-	expectedErrorMessage := "Function has no associated image. Has it been built?"
-	if err == nil || err.Error() != expectedErrorMessage {
-		t.Fatalf("Expected error '%v', got '%v'", expectedErrorMessage, err)
+	var noImageErr docker.ErrNoImage
+	if !errors.As(err, &noImageErr) {
+		t.Fatalf("expected ErrNoImage, got %v", err)
 	}
 }