set up vm_test to direct all output to a pipe

Sadly, the original sin of os.Std{in,out,err} requires
an os.File, else we could use an in-memory pipe.

Signed-off-by: Ronald G Minnich <rminnich@gmail.com>

Author: rminnich

initramfs/vm_test.go

@@ -9,10 +9,12 @@ package initramfs_test
 import (
 	"context"
 	"errors"
+	"io"
 	"os"
 	"path/filepath"
 	"testing"
 
+	"github.com/u-root/cpu/client"
 	"github.com/u-root/cpu/initramfs"
 )
 
@@ -57,11 +59,19 @@ func TestCPU(t *testing.T) {
 		if err != nil {
 			t.Fatalf("CPUCommand: got %v, want nil", err)
 		}
+		client.SetVerbose(t.Logf)
+		r, w, err := os.Pipe()
+		cpu.Stdout, cpu.Stderr = w, w
 
 		err = cpu.Run()
 		if err == nil != tt.ok {
 			t.Errorf("%s %s: got %v, want %v", tt.cmd, tt.args, err == nil != tt.ok, err == nil == tt.ok)
 		}
+		b, err := io.ReadAll(r)
+		if err != nil {
+			t.Errorf("reading pipe output: got %v, want nil", err)
+		}
+		t.Logf("%q", string(b))
 	}
 	b, err := os.ReadFile(filepath.Join(d, "b"))
 	if err != nil {