logtesting

var stdout, stderr *os.File = os.Stdout, os.Stderr

var (
	t = &testing.T{}
	c = Capture(t)
)

fmt.Fprintln(os.Stdout, "foo")
fmt.Fprintln(os.Stderr, "bar")
fmt.Fprintln(os.Stderr, "baz")

fmt.Fprintf(stdout, "stdout swapped: %t\n", stdout != os.Stdout)
fmt.Fprintf(stdout, "stderr swapped: %t\n", stderr != os.Stderr)
fmt.Fprintf(stdout, "stdout: "+c.Stdout(t))
fmt.Fprintf(stdout, "stderr: "+c.Stderr(t))

Output:

stdout swapped: true
stderr swapped: true
stdout: foo
stderr: bar
baz