Fix code comment and add tests for STDIN reads

internal/utils/io.go

@@ -18,30 +18,30 @@ func maybeUnwrap(err error) error {
 	return err
 }
 
-// stdinFilename is the name of the file that is used in many command line utilities
-// to denote input is to be read from STDIN.
+// stdinFilename is the name of the file that is used in many command
+// line utilities to denote input is to be read from STDIN.
 const stdinFilename = "-"
 
-// stdin points to os.Stdin.
+// stdin points to STDIN through os.Stdin.
 var stdin = os.Stdin
 
-// ReadFile reads the file named by filename and returns the
-// contents. If filename is equal to "-", it will read from
+// ReadFile reads the file identified by filename and returns
+// the contents. If filename is equal to "-", it will read from
 // STDIN.
-func ReadFile(name string) (b []byte, err error) {
-	if name == stdinFilename {
-		name = "/dev/stdin"
+func ReadFile(filename string) (b []byte, err error) {
+	if filename == stdinFilename {
+		filename = "/dev/stdin"
 		b, err = io.ReadAll(stdin)
 	} else {
 		var contents []byte
-		contents, err = os.ReadFile(name)
+		contents, err = os.ReadFile(filename)
 		if err != nil {
-			return nil, errors.Wrapf(maybeUnwrap(err), "error reading %s", name)
+			return nil, errors.Wrapf(maybeUnwrap(err), "error reading %q", filename)
 		}
 		b, err = io.ReadAll(utfbom.SkipOnly(bytes.NewReader(contents)))
 	}
 	if err != nil {
-		return nil, errors.Wrapf(maybeUnwrap(err), "error reading %s", name)
+		return nil, errors.Wrapf(maybeUnwrap(err), "error reading %q", filename)
 	}
 	return
 }

internal/utils/io_test.go

@@ -2,15 +2,18 @@ package utils
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
 	"reflect"
 	"testing"
 
 	"github.com/pkg/errors"
+	"github.com/stretchr/testify/require"
 )
 
 func TestReadFile(t *testing.T) {
+	t.Parallel()
 	type args struct {
 		filename string
 	}
@@ -37,7 +40,64 @@ func TestReadFile(t *testing.T) {
 	}
 }
 
+// Set content to be read from mock STDIN
+func setStdinContent(t *testing.T, content string) (cleanup func()) {
+	f, err := os.CreateTemp("" /* dir */, "utils-read-test")
+	require.NoError(t, err)
+	_, err = f.Write([]byte(content))
+	require.NoError(t, err)
+	_, err = f.Seek(0, io.SeekStart)
+	require.NoError(t, err)
+	old := stdin
+	stdin = f
+
+	return func() {
+		stdin = old
+		require.NoError(t, f.Close())
+		require.NoError(t, os.Remove(f.Name()))
+	}
+}
+
+func TestReadFromStdin(t *testing.T) {
+	cleanup := setStdinContent(t, "input on STDIN")
+	t.Cleanup(func() {
+		cleanup()
+	})
+
+	b, err := ReadFile(stdinFilename)
+	require.NoError(t, err)
+	require.Equal(t, "input on STDIN", string(b))
+}
+
+// Sets STDIN to a file that is already closed, and thus fails
+// to be read from.
+func setFailingStdin(t *testing.T) (cleanup func()) {
+	f, err := os.CreateTemp("" /* dir */, "utils-read-test")
+	require.NoError(t, err)
+	err = f.Close()
+	require.NoError(t, err)
+	old := stdin
+	stdin = f
+
+	return func() {
+		stdin = old
+		require.NoError(t, os.Remove(f.Name()))
+	}
+}
+
+func TestReadFromStdinFails(t *testing.T) {
+	cleanup := setFailingStdin(t)
+	t.Cleanup(func() {
+		cleanup()
+	})
+
+	b, err := ReadFile(stdinFilename)
+	require.Error(t, err)
+	require.Empty(t, b)
+}
+
 func TestReadPasswordFromFile(t *testing.T) {
+	t.Parallel()
 	type args struct {
 		filename string
 	}
@@ -65,11 +125,20 @@ func TestReadPasswordFromFile(t *testing.T) {
 	}
 }
 
+func TestReadPasswordFromStdin(t *testing.T) {
+	cleanup := setStdinContent(t, "this-is-a-secret-testing-password")
+	t.Cleanup(func() {
+		cleanup()
+	})
+
+	b, err := ReadPasswordFromFile(stdinFilename)
+	require.NoError(t, err)
+	require.Equal(t, "this-is-a-secret-testing-password", string(b))
+}
+
 func TestWriteFile(t *testing.T) {
 	tmpDir, err := os.MkdirTemp(os.TempDir(), "go-tests")
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
 	t.Cleanup(func() {
 		os.RemoveAll(tmpDir)
 	})
@@ -97,6 +166,7 @@ func TestWriteFile(t *testing.T) {
 }
 
 func Test_maybeUnwrap(t *testing.T) {
+	t.Parallel()
 	wantErr := fmt.Errorf("the error")
 
 	type args struct {