vfstests: move functional tests from mountlib and make them work with VFS

The tests are now run for the mount commands and for the plain VFS.

This makes the tests much easier to debug when running with a VFS than
through a mount.

vfs/vfstest/file.go

@@ -0,0 +1,74 @@
+package vfstest
+
+import (
+	"os"
+	"runtime"
+	"testing"
+	"time"
+
+	"github.com/rclone/rclone/vfs"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestFileModTime tests mod times on files
+func TestFileModTime(t *testing.T) {
+	run.skipIfNoFUSE(t)
+
+	run.createFile(t, "file", "123")
+
+	mtime := time.Date(2012, time.November, 18, 17, 32, 31, 0, time.UTC)
+	err := run.os.Chtimes(run.path("file"), mtime, mtime)
+	require.NoError(t, err)
+
+	info, err := run.os.Stat(run.path("file"))
+	require.NoError(t, err)
+
+	// avoid errors because of timezone differences
+	assert.Equal(t, info.ModTime().Unix(), mtime.Unix())
+
+	run.rm(t, "file")
+}
+
+// run.os.Create without opening for write too
+func osCreate(name string) (vfs.OsFiler, error) {
+	return run.os.OpenFile(name, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
+}
+
+// run.os.Create with append
+func osAppend(name string) (vfs.OsFiler, error) {
+	return run.os.OpenFile(name, os.O_WRONLY|os.O_APPEND, 0666)
+}
+
+// TestFileModTimeWithOpenWriters tests mod time on open files
+func TestFileModTimeWithOpenWriters(t *testing.T) {
+	run.skipIfNoFUSE(t)
+	if runtime.GOOS == "windows" {
+		t.Skip("Skipping test on Windows")
+	}
+
+	mtime := time.Date(2012, time.November, 18, 17, 32, 31, 0, time.UTC)
+	filepath := run.path("cp-archive-test")
+
+	f, err := osCreate(filepath)
+	require.NoError(t, err)
+
+	_, err = f.Write([]byte{104, 105})
+	require.NoError(t, err)
+
+	err = run.os.Chtimes(filepath, mtime, mtime)
+	require.NoError(t, err)
+
+	err = f.Close()
+	require.NoError(t, err)
+
+	run.waitForWriters()
+
+	info, err := run.os.Stat(filepath)
+	require.NoError(t, err)
+
+	// avoid errors because of timezone differences
+	assert.Equal(t, info.ModTime().Unix(), mtime.Unix())
+
+	run.rm(t, "cp-archive-test")
+}