Update MongoDB tests to not fail in Go 1.16 (#11533)

# Conflicts:
#	.circleci/config.yml
#	.circleci/config/commands/go_test.yml

go.mod

@@ -51,6 +51,7 @@ require (
 	github.com/go-test/deep v1.0.7
 	github.com/gocql/gocql v0.0.0-20210401103645-80ab1e13e309
 	github.com/golang/protobuf v1.4.2
+	github.com/google/go-cmp v0.5.5
 	github.com/google/go-github v17.0.0+incompatible
 	github.com/google/go-metrics-stackdriver v0.2.0
 	github.com/hashicorp/consul-template v0.25.2

plugins/database/mongodb/mongodb_test.go

@@ -7,9 +7,13 @@ import (
 	"fmt"
 	"reflect"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
+	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
+
 	"github.com/hashicorp/vault/helper/testhelpers/certhelpers"
 	"github.com/hashicorp/vault/helper/testhelpers/mongodb"
 	dbplugin "github.com/hashicorp/vault/sdk/database/dbplugin/v5"
@@ -346,9 +350,7 @@ func TestGetTLSAuth(t *testing.T) {
 			if !test.expectErr && err != nil {
 				t.Fatalf("no error expected, got: %s", err)
 			}
-			if !reflect.DeepEqual(actual, test.expectOpts) {
-				t.Fatalf("Actual:\n%#v\nExpected:\n%#v", actual, test.expectOpts)
-			}
+			assertDeepEqual(t, test.expectOpts, actual)
 		})
 	}
 }
@@ -363,6 +365,27 @@ func appendToCertPool(t *testing.T, pool *x509.CertPool, caPem []byte) *x509.Cer
 	return pool
 }
 
+var cmpClientOptionsOpts = cmp.Options{
+	cmp.AllowUnexported(options.ClientOptions{}),
+
+	cmp.AllowUnexported(tls.Config{}),
+	cmpopts.IgnoreTypes(sync.Mutex{}, sync.RWMutex{}),
+
+	// 'lazyCerts' has a func field which can't be compared.
+	cmpopts.IgnoreFields(x509.CertPool{}, "lazyCerts"),
+	cmp.AllowUnexported(x509.CertPool{}),
+}
+
+// Need a special comparison for ClientOptions because reflect.DeepEquals won't work in Go 1.16.
+// See: https://github.com/golang/go/issues/45891
+func assertDeepEqual(t *testing.T, a, b *options.ClientOptions) {
+	t.Helper()
+
+	if diff := cmp.Diff(a, b, cmpClientOptionsOpts); diff != "" {
+		t.Fatalf("assertion failed: values are not equal\n--- expected\n+++ actual\n%v", diff)
+	}
+}
+
 func createDBUser(t testing.TB, connURL, db, username, password string) {
 	t.Helper()