VAULT-15547 Agent/proxy decoupling, take two (#20634)

* VAULT-15547 Additional tests, refactoring, for proxy split

* VAULT-15547 Additional tests, refactoring, for proxy split

* VAULT-15547 Import reorganization

* VAULT-15547 Some missed updates for PersistConfig

* VAULT-15547 address comments

* VAULT-15547 address comments

command/agentproxyshared/helpers_test.go

@@ -0,0 +1,92 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package agentproxyshared
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	hclog "github.com/hashicorp/go-hclog"
+	"github.com/hashicorp/vault/api"
+	"github.com/hashicorp/vault/command/agentproxyshared/cache"
+	"github.com/hashicorp/vault/sdk/helper/logging"
+)
+
+func testNewLeaseCache(t *testing.T, responses []*cache.SendResponse) *cache.LeaseCache {
+	t.Helper()
+
+	client, err := api.NewClient(api.DefaultConfig())
+	if err != nil {
+		t.Fatal(err)
+	}
+	lc, err := cache.NewLeaseCache(&cache.LeaseCacheConfig{
+		Client:      client,
+		BaseContext: context.Background(),
+		Proxier:     cache.NewMockProxier(responses),
+		Logger:      logging.NewVaultLogger(hclog.Trace).Named("cache.leasecache"),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return lc
+}
+
+func populateTempFile(t *testing.T, name, contents string) *os.File {
+	t.Helper()
+
+	file, err := os.CreateTemp(t.TempDir(), name)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = file.WriteString(contents)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = file.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return file
+}
+
+// Test_AddPersistentStorageToLeaseCache Tests that AddPersistentStorageToLeaseCache() correctly
+// adds persistent storage to a lease cache
+func Test_AddPersistentStorageToLeaseCache(t *testing.T) {
+	tempDir := t.TempDir()
+	serviceAccountTokenFile := populateTempFile(t, "proxy-config.hcl", "token")
+
+	persistConfig := &PersistConfig{
+		Type:                    "kubernetes",
+		Path:                    tempDir,
+		KeepAfterImport:         false,
+		ExitOnErr:               false,
+		ServiceAccountTokenFile: serviceAccountTokenFile.Name(),
+	}
+
+	leaseCache := testNewLeaseCache(t, nil)
+	if leaseCache.PersistentStorage() != nil {
+		t.Fatal("persistent storage was available before ours was added")
+	}
+
+	deferFunc, token, err := AddPersistentStorageToLeaseCache(context.Background(), leaseCache, persistConfig, logging.NewVaultLogger(hclog.Info))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if leaseCache.PersistentStorage() == nil {
+		t.Fatal("persistent storage was not added")
+	}
+
+	if token != "" {
+		t.Fatal("expected token to be empty")
+	}
+
+	if deferFunc == nil {
+		t.Fatal("expected deferFunc to not be nil")
+	}
+}