Update FakeCli to remove duplication in tests.

Use byte buffers by default, since that is what is done most of the time.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

cli/internal/test/cli.go

@@ -1,6 +1,7 @@
 package test
 
 import (
+	"bytes"
 	"io"
 	"io/ioutil"
 	"strings"
@@ -16,17 +17,29 @@ type FakeCli struct {
 	client     client.APIClient
 	configfile *configfile.ConfigFile
 	out        *command.OutStream
-	err        io.Writer
+	outBuffer  *bytes.Buffer
+	err        *bytes.Buffer
 	in         *command.InStream
 	server     command.ServerInfo
 }
 
-// NewFakeCli returns a Cli backed by the fakeCli
-func NewFakeCli(client client.APIClient, out io.Writer) *FakeCli {
+// NewFakeCliWithOutput returns a Cli backed by the fakeCli
+// Deprecated: Use NewFakeCli
+func NewFakeCliWithOutput(client client.APIClient, out io.Writer) *FakeCli {
+	cli := NewFakeCli(client)
+	cli.out = command.NewOutStream(out)
+	return cli
+}
+
+// NewFakeCli returns a fake for the command.Cli interface
+func NewFakeCli(client client.APIClient) *FakeCli {
+	outBuffer := new(bytes.Buffer)
+	errBuffer := new(bytes.Buffer)
 	return &FakeCli{
 		client:     client,
-		out:        command.NewOutStream(out),
-		err:        ioutil.Discard,
+		out:        command.NewOutStream(outBuffer),
+		outBuffer:  outBuffer,
+		err:        errBuffer,
 		in:         command.NewInStream(ioutil.NopCloser(strings.NewReader(""))),
 		configfile: configfile.New("configfile"),
 	}
@@ -38,7 +51,7 @@ func (c *FakeCli) SetIn(in *command.InStream) {
 }
 
 // SetErr sets the stderr stream for the cli to the specified io.Writer
-func (c *FakeCli) SetErr(err io.Writer) {
+func (c *FakeCli) SetErr(err *bytes.Buffer) {
 	c.err = err
 }
 
@@ -76,3 +89,13 @@ func (c *FakeCli) ConfigFile() *configfile.ConfigFile {
 func (c *FakeCli) ServerInfo() command.ServerInfo {
 	return c.server
 }
+
+// OutBuffer returns the stdout buffer
+func (c *FakeCli) OutBuffer() *bytes.Buffer {
+	return c.outBuffer
+}
+
+// ErrBuffer Buffer returns the stderr buffer
+func (c *FakeCli) ErrBuffer() *bytes.Buffer {
+	return c.err
+}