Refactor formatting of output

This change is almost perfectly compatible with the existing code,
except it's a little shorter because it uses a list of a available
formatters that must implement a `command.Formatter` interface.

Also added some basic formatting tests.

command/format_test.go

@@ -0,0 +1,81 @@
+package command
+
+import (
+	"encoding/json"
+	"github.com/ghodss/yaml"
+	"github.com/hashicorp/vault/api"
+	"strings"
+	"testing"
+)
+
+var output string
+
+type mockUi struct {
+	t          *testing.T
+	SampleData string
+}
+
+func (m mockUi) Ask(_ string) (string, error) {
+	m.t.FailNow()
+	return "", nil
+}
+func (m mockUi) AskSecret(_ string) (string, error) {
+	m.t.FailNow()
+	return "", nil
+}
+func (m mockUi) Output(s string) {
+	output = s
+}
+func (m mockUi) Info(s string) {
+	m.t.Log(s)
+}
+func (m mockUi) Error(s string) {
+	m.t.Log(s)
+}
+func (m mockUi) Warn(s string) {
+	m.t.Log(s)
+}
+
+func TestJsonFormatter(t *testing.T) {
+	ui := mockUi{t: t, SampleData: "something"}
+	if err := outputWithFormat(ui, "json", ui); err != 0 {
+		t.Fatal(err)
+	}
+	var newUi mockUi
+	if err := json.Unmarshal([]byte(output), &newUi); err != nil {
+		t.Fatal(err)
+	}
+	if newUi.SampleData != ui.SampleData {
+		t.Fatalf(`values not equal ("%s" != "%s")`,
+			newUi.SampleData,
+			ui.SampleData)
+	}
+}
+
+func TestYamlFormatter(t *testing.T) {
+	ui := mockUi{t: t, SampleData: "something"}
+	if err := outputWithFormat(ui, "yaml", ui); err != 0 {
+		t.Fatal(err)
+	}
+	var newUi mockUi
+	err := yaml.Unmarshal([]byte(output), &newUi)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if newUi.SampleData != ui.SampleData {
+		t.Fatalf(`values not equal ("%s" != "%s")`,
+			newUi.SampleData,
+			ui.SampleData)
+	}
+}
+
+func TestTableFormatter(t *testing.T) {
+	ui := mockUi{t: t}
+	s := api.Secret{Data: map[string]interface{}{"k": "something"}}
+	if err := outputWithFormat(ui, "table", &s); err != 0 {
+		t.Fatal(err)
+	}
+	if !strings.Contains(output, "something") {
+		t.Fatal("did not find something")
+	}
+}