diff --git a/fs/cache/cache_test.go b/fs/cache/cache_test.go
index f4e5eb9c2..210fcddbf 100644
--- a/fs/cache/cache_test.go
+++ b/fs/cache/cache_test.go
@@ -23,9 +23,11 @@ func mockNewFs(t *testing.T) func(ctx context.Context, path string) (fs.Fs, erro
 		called++
 		switch path {
 		case "mock:/":
-			return mockfs.NewFs(ctx, "mock", "/"), nil
+			return mockfs.NewFs(ctx, "mock", "/", nil)
 		case "mock:/file.txt", "mock:file.txt":
-			return mockfs.NewFs(ctx, "mock", "/"), fs.ErrorIsFile
+			fMock, err := mockfs.NewFs(ctx, "mock", "/", nil)
+			require.NoError(t, err)
+			return fMock, fs.ErrorIsFile
 		case "mock:/error":
 			return nil, errSentinel
 		}
@@ -117,7 +119,8 @@ func TestGetError(t *testing.T) {
 func TestPut(t *testing.T) {
 	create := mockNewFs(t)
 
-	f := mockfs.NewFs(context.Background(), "mock", "/alien")
+	f, err := mockfs.NewFs(context.Background(), "mock", "/alien", nil)
+	require.NoError(t, err)
 
 	assert.Equal(t, 0, Entries())
 
@@ -147,7 +150,8 @@ func TestPin(t *testing.T) {
 	create := mockNewFs(t)
 
 	// Test pinning and unpinning nonexistent
-	f := mockfs.NewFs(context.Background(), "mock", "/alien")
+	f, err := mockfs.NewFs(context.Background(), "mock", "/alien", nil)
+	require.NoError(t, err)
 	Pin(f)
 	Unpin(f)
 
diff --git a/fs/fingerprint_test.go b/fs/fingerprint_test.go
index 0a69ceddf..713baf4cb 100644
--- a/fs/fingerprint_test.go
+++ b/fs/fingerprint_test.go
@@ -10,11 +10,14 @@ import (
 	"github.com/rclone/rclone/fstest/mockfs"
 	"github.com/rclone/rclone/fstest/mockobject"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestFingerprint(t *testing.T) {
 	ctx := context.Background()
-	f := mockfs.NewFs(ctx, "test", "root")
+	fMock, err := mockfs.NewFs(ctx, "test", "root", nil)
+	require.NoError(t, err)
+	f := fMock.(*mockfs.Fs)
 	f.SetHashes(hash.NewHashSet(hash.MD5))
 
 	for i, test := range []struct {
diff --git a/fs/operations/multithread_test.go b/fs/operations/multithread_test.go
index a036139e5..fa982cf59 100644
--- a/fs/operations/multithread_test.go
+++ b/fs/operations/multithread_test.go
@@ -19,9 +19,11 @@ import (
 func TestDoMultiThreadCopy(t *testing.T) {
 	ctx := context.Background()
 	ci := fs.GetConfig(ctx)
-	f := mockfs.NewFs(ctx, "potato", "")
+	f, err := mockfs.NewFs(ctx, "potato", "", nil)
+	require.NoError(t, err)
 	src := mockobject.New("file.txt").WithContent([]byte(random.String(100)), mockobject.SeekModeNone)
-	srcFs := mockfs.NewFs(ctx, "sausage", "")
+	srcFs, err := mockfs.NewFs(ctx, "sausage", "", nil)
+	require.NoError(t, err)
 	src.SetFs(srcFs)
 
 	oldStreams := ci.MultiThreadStreams
diff --git a/fs/rc/cache_test.go b/fs/rc/cache_test.go
index bbda7e0b6..6d7c7730e 100644
--- a/fs/rc/cache_test.go
+++ b/fs/rc/cache_test.go
@@ -12,7 +12,8 @@ import (
 )
 
 func mockNewFs(t *testing.T) func() {
-	f := mockfs.NewFs(context.Background(), "mock", "mock")
+	f, err := mockfs.NewFs(context.Background(), "mock", "mock", nil)
+	require.NoError(t, err)
 	cache.Put("/", f)
 	cache.Put("mock:/", f)
 	cache.Put(":mock:/", f)
diff --git a/fs/walk/walk_test.go b/fs/walk/walk_test.go
index cbfa82ce8..d47991486 100644
--- a/fs/walk/walk_test.go
+++ b/fs/walk/walk_test.go
@@ -798,7 +798,8 @@ func TestListR(t *testing.T) {
 		mockobject.Object("dir/b"),
 		mockobject.Object("dir/c"),
 	}
-	f := mockfs.NewFs(ctx, "mock", "/")
+	f, err := mockfs.NewFs(ctx, "mock", "/", nil)
+	require.NoError(t, err)
 	var got []string
 	clearCallback := func() {
 		got = nil
diff --git a/fstest/mockfs/mockfs.go b/fstest/mockfs/mockfs.go
index 62489c2f6..68df1f6b4 100644
--- a/fstest/mockfs/mockfs.go
+++ b/fstest/mockfs/mockfs.go
@@ -10,9 +10,24 @@ import (
 	"time"
 
 	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/config/configmap"
 	"github.com/rclone/rclone/fs/hash"
 )
 
+// Register with Fs
+func Register() {
+	fs.Register(&fs.RegInfo{
+		Name:        "mockfs",
+		Description: "Mock FS",
+		NewFs:       NewFs,
+		Options: []fs.Option{{
+			Name:     "potato",
+			Help:     "Does it have a potato?.",
+			Required: true,
+		}},
+	})
+}
+
 // Fs is a minimal mock Fs
 type Fs struct {
 	name     string        // the name of the remote
@@ -26,13 +41,13 @@ type Fs struct {
 var ErrNotImplemented = errors.New("not implemented")
 
 // NewFs returns a new mock Fs
-func NewFs(ctx context.Context, name, root string) *Fs {
+func NewFs(ctx context.Context, name string, root string, config configmap.Mapper) (fs.Fs, error) {
 	f := &Fs{
 		name: name,
 		root: root,
 	}
 	f.features = (&fs.Features{}).Fill(ctx, f)
-	return f
+	return f, nil
 }
 
 // AddObject adds an Object for List to return
diff --git a/vfs/file_test.go b/vfs/file_test.go
index 728d8c699..6688749d2 100644
--- a/vfs/file_test.go
+++ b/vfs/file_test.go
@@ -193,7 +193,9 @@ func TestFileOpenReadUnknownSize(t *testing.T) {
 	assert.Equal(t, int64(-1), o.Size())
 
 	// add it to a mock fs
-	f := mockfs.NewFs(context.Background(), "test", "root")
+	fMock, err := mockfs.NewFs(context.Background(), "test", "root", nil)
+	require.NoError(t, err)
+	f := fMock.(*mockfs.Fs)
 	f.AddObject(o)
 	testObj, err := f.NewObject(ctx, remote)
 	require.NoError(t, err)