Add test for stdin input

Shamelessly borrowed this pattern from write_test.go

command/auth.go

@@ -27,6 +27,9 @@ type AuthCommand struct {
 	Meta
 
 	Handlers map[string]AuthHandler
+
+	// The fields below can be overwritten for tests
+	testStdin io.Reader
 }
 
 func (c *AuthCommand) Run(args []string) int {
@@ -66,9 +69,15 @@ func (c *AuthCommand) Run(args []string) int {
 	// token is where the final token will go
 	handler := c.Handlers[method]
 
+	// Read token from stdin if first arg is exactly "-"
+	var stdin io.Reader = os.Stdin
+	if c.testStdin != nil {
+		stdin = c.testStdin
+	}
+
 	if len(args) > 0 && args[0] == "-" {
-		stdin := bufio.NewReader(os.Stdin)
-		args[0], err = stdin.ReadString('\n')
+		stdinR := bufio.NewReader(stdin)
+		args[0], err = stdinR.ReadString('\n')
 		if err != nil && err != io.EOF {
 			c.Ui.Error(fmt.Sprintf("Error reading from stdin: %s", err))
 			return 1

command/auth_test.go

@@ -2,6 +2,7 @@ package command
 
 import (
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -82,6 +83,36 @@ func TestAuth_token(t *testing.T) {
 	}
 }
 
+func TestAuth_stdin(t *testing.T) {
+	core, _, token := vault.TestCoreUnsealed(t)
+	ln, addr := http.TestServer(t, core)
+	defer ln.Close()
+
+	testAuthInit(t)
+
+	stdinR, stdinW := io.Pipe()
+	ui := new(cli.MockUi)
+	c := &AuthCommand{
+		Meta: Meta{
+			Ui: ui,
+		},
+		testStdin: stdinR,
+	}
+
+	go func() {
+		stdinW.Write([]byte(token))
+		stdinW.Close()
+	}()
+
+	args := []string{
+		"-address", addr,
+		"-",
+	}
+	if code := c.Run(args); code != 0 {
+		t.Fatalf("bad: %d\n\n%s", code, ui.ErrorWriter.String())
+	}
+}
+
 func TestAuth_badToken(t *testing.T) {
 	core, _, _ := vault.TestCoreUnsealed(t)
 	ln, addr := http.TestServer(t, core)