Fix error handling and message when the App to render does not exist

Signed-off-by: Jean-Christophe Sirot <jean-christophe.sirot@docker.com>

Author: Jean-Christophe Sirot

e2e/commands_test.go

@@ -75,16 +75,14 @@ func testRenderApp(appPath string, env ...string) func(*testing.T) {
 	}
 }
 
-func TestRenderAppDirectoryFails(t *testing.T) {
+func TestRenderAppNotFound(t *testing.T) {
 	cmd, cleanup := dockerCli.createTestCmd()
 	defer cleanup()
-	appPath := filepath.Join("testdata", "envfile", "envfile.dockerapp")
 
-	cmd.Command = dockerCli.Command("app", "render", appPath)
-	icmd.RunCmd(cmd).Assert(t, icmd.Expected{
-		ExitCode: 1,
-		Err:      fmt.Sprintf("%q looks like a docker App directory and App must be built first before rendering", appPath),
-	})
+	appName := "non_existing_app:some_tag"
+	cmd.Command = dockerCli.Command("app", "render", appName)
+	checkContains(t, icmd.RunCmd(cmd).Assert(t, icmd.Expected{ExitCode: 1}).Combined(),
+		[]string{fmt.Sprintf("could not render %q: no such App image", appName)})
 }
 
 func TestRenderFormatters(t *testing.T) {

internal/commands/render.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"io"
 	"os"
-	"strings"
 
 	"github.com/deislabs/cnab-go/action"
 	"github.com/docker/app/internal"
@@ -14,6 +13,7 @@ import (
 	"github.com/docker/cli/cli"
 	"github.com/docker/cli/cli/command"
 	"github.com/docker/cli/cli/config"
+	"github.com/pkg/errors"
 	"github.com/spf13/cobra"
 )
 
@@ -78,10 +78,7 @@ func prepareCustomAction(actionName string, dockerCli command.Cli, appname strin
 	}
 	bundle, ref, err := cnab.GetBundle(dockerCli, bundleStore, appname)
 	if err != nil {
-		if strings.HasSuffix(appname, ".dockerapp") {
-			return nil, nil, nil, fmt.Errorf("%q looks like a docker App directory and App must be built first before rendering", appname)
-		}
-		return nil, nil, nil, err
+		return nil, nil, nil, errors.Wrapf(err, "could not render %q: no such App image", appname)
 	}
 	installation, err := appstore.NewInstallation("custom-action", ref.String())
 	if err != nil {