main: unif/refactor std{out,err} test handling

For historic reasons we have two way to test the std{out,err}
output. One is to just monkey patch `var osStdout = os.Stdout`
and then replace it in the tests, the other to have a helper
that works like a `with` in python that replaces the stdout/stderr
dynamically, e.g.:

```
stdout, stderr := testutil.CaptureStdio(t, func() {
 err = main.Run()
 require.NoError(t, err)
})
```

The trouble is that they are not quite compatible. In places
where we use the monkey patches `osStdout` the
testutil.CaptureStdio() will not work as it (temporarely)
replaces the "real" `os.Stdout` (and vice-versa).

So this commit unifies all tests to use testutil.CaptureStdio()
which feels slightly nicer than the other approach in the
sense that one does not need to remember to use `osStdout` in
the code. Its mostly mechanical.

Co-authored-by: Lukas Zapletal <lzap+git@redhat.com>

Author: mvo5

cmd/image-builder/bib_cloud.go

@@ -42,11 +42,11 @@ func bibUpload(uploader cloud.Uploader, path string, flags *pflag.FlagSet) error
 		size = st.Size()
 		pbar.SetTotal(size)
 		pbar.Set(pb.Bytes, true)
-		pbar.SetWriter(osStdout)
+		pbar.SetWriter(os.Stdout)
 		r = pbar.NewProxyReader(file)
 		pbar.Start()
 		defer pbar.Finish()
 	}
 
-	return uploader.UploadAndRegister(r, uint64(size), osStderr)
+	return uploader.UploadAndRegister(r, uint64(size), os.Stderr)
 }

cmd/image-builder/distro.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"os"
 
 	"github.com/osbuild/images/pkg/distro"
 )
@@ -25,6 +26,6 @@ func findDistro(argDistroName, bpDistroName string) (string, error) {
 	if err != nil {
 		return "", fmt.Errorf("error deriving host distro %w", err)
 	}
-	fmt.Fprintf(osStderr, "No distro name specified, selecting %q based on host, use --distro to override\n", distroStr)
+	fmt.Fprintf(os.Stderr, "No distro name specified, selecting %q based on host, use --distro to override\n", distroStr)
 	return distroStr, nil
 }

cmd/image-builder/distro_test.go

@@ -1,12 +1,12 @@
 package main_test
 
 import (
-	"bytes"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 
 	main "github.com/osbuild/image-builder-cli/cmd/image-builder"
+	"github.com/osbuild/image-builder-cli/internal/testutil"
 )
 
 func TestFindDistro(t *testing.T) {
@@ -32,17 +32,17 @@ func TestFindDistro(t *testing.T) {
 }
 
 func TestFindDistroAutoDetect(t *testing.T) {
-	var buf bytes.Buffer
-	restore := main.MockOsStderr(&buf)
-	defer restore()
-
-	restore = main.MockDistroGetHostDistroName(func() (string, error) {
+	restore := main.MockDistroGetHostDistroName(func() (string, error) {
 		return "mocked-host-distro", nil
 	})
 	defer restore()
 
-	distro, err := main.FindDistro("", "")
+	var err error
+	var distro string
+	_, stderr := testutil.CaptureStdio(t, func() {
+		distro, err = main.FindDistro("", "")
+	})
 	assert.NoError(t, err)
 	assert.Equal(t, "mocked-host-distro", distro)
-	assert.Equal(t, "No distro name specified, selecting \"mocked-host-distro\" based on host, use --distro to override\n", buf.String())
+	assert.Equal(t, "No distro name specified, selecting \"mocked-host-distro\" based on host, use --distro to override\n", stderr)
 }

cmd/image-builder/export_test.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"fmt"
-	"io"
 	"os"
 
 	"github.com/osbuild/images/pkg/cloud"
@@ -31,22 +30,6 @@ func MockOsArgs(new []string) (restore func()) {
 	}
 }
 
-func MockOsStdout(new io.Writer) (restore func()) {
-	saved := osStdout
-	osStdout = new
-	return func() {
-		osStdout = saved
-	}
-}
-
-func MockOsStderr(new io.Writer) (restore func()) {
-	saved := osStderr
-	osStderr = new
-	return func() {
-		osStderr = saved
-	}
-}
-
 func MockNewRepoRegistry(f func() (*reporegistry.RepoRegistry, error)) (restore func()) {
 	saved := newRepoRegistry
 	newRepoRegistry = func(repoDir string, extraRepos []string) (*reporegistry.RepoRegistry, error) {

cmd/image-builder/list.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	"os"
+
 	"github.com/osbuild/images/pkg/imagefilter"
 )
 
@@ -19,7 +21,7 @@ func listImages(repoDir string, extraRepos []string, output string, filterExprs
 	if err != nil {
 		return err
 	}
-	if err := fmter.Output(osStdout, filteredResult); err != nil {
+	if err := fmter.Output(os.Stdout, filteredResult); err != nil {
 		return err
 	}
 

cmd/image-builder/main.go

@@ -30,11 +30,6 @@ import (
 	"github.com/osbuild/image-builder-cli/pkg/setup"
 )
 
-var (
-	osStdout io.Writer = os.Stdout
-	osStderr io.Writer = os.Stderr
-)
-
 // basenameFor returns the basename for directory and filenames
 // for the given imageType. This can be user overriden via userBasename.
 func basenameFor(img *imagefilter.Result, userBasename string) string {
@@ -340,7 +335,7 @@ func cmdManifest(cmd *cobra.Command, args []string) error {
 	if err != nil {
 		return err
 	}
-	_, err = cmdManifestWrapper(pbar, cmd, args, osStdout, io.Discard, nil)
+	_, err = cmdManifestWrapper(pbar, cmd, args, os.Stdout, io.Discard, nil)
 	return err
 }
 
@@ -452,7 +447,7 @@ func cmdBuild(cmd *cobra.Command, args []string) error {
 	}
 	pbar.Stop()
 
-	fmt.Fprintf(osStdout, "Image build successful: %s\n", imagePath)
+	fmt.Fprintf(os.Stdout, "Image build successful: %s\n", imagePath)
 
 	if uploader != nil {
 		// XXX: integrate better into the progress, see bib
@@ -493,7 +488,7 @@ func cmdDescribeImg(cmd *cobra.Command, args []string) error {
 		return err
 	}
 
-	return describeImage(res, osStdout)
+	return describeImage(res, os.Stdout)
 }
 
 func normalizeRootArgs(_ *pflag.FlagSet, name string) pflag.NormalizedName {
@@ -549,9 +544,6 @@ operating systems like Fedora, CentOS and RHEL with easy customizations support.
 	rootCmd.PersistentFlags().String("output-dir", "", `Put output into the specified directory`)
 	rootCmd.PersistentFlags().BoolP("verbose", "v", false, `Switch to verbose mode (more logging on stderr and verbose progress)`)
 
-	rootCmd.SetOut(osStdout)
-	rootCmd.SetErr(osStderr)
-
 	listCmd := &cobra.Command{
 		Use:          "list",
 		Short:        "List buildable images, use --filter to limit further",