fix MemoryDevice::list & update filesystem tests

dev/tests/memory_filesystem.lua

@@ -1,12 +1,15 @@
 app.create_memory_device("memtest")
+local tmp = file.create_memory_device()
 
 debug.log("check initial state")
 assert(file.exists("memtest:"))
 assert(file.is_writeable("memtest:"))
+assert(file.is_writeable(tmp..":"))
 
 debug.log("write text file")
 assert(file.write("memtest:text.txt", "example, пример"))
 assert(file.exists("memtest:text.txt"))
+assert(file.isfile("memtest:text.txt"))
 
 debug.log("read text file")
 assert(file.read("memtest:text.txt") == "example, пример")
@@ -27,6 +30,17 @@ debug.log("create directories")
 file.mkdirs("memtest:dir/subdir/other")
 assert(file.isdir("memtest:dir/subdir/other"))
 
+debug.log("list directory")
+file.write("memtest:dir/subdir/a.txt", "helloworld")
+file.write("memtest:dir/subdir/b.txt", "gfgsfhs")
+
+local entries = file.list("memtest:dir/subdir")
+assert(#entries == 3)
+table.sort(entries)
+assert(entries[1] == "memtest:dir/subdir/a.txt")
+assert(entries[2] == "memtest:dir/subdir/b.txt")
+assert(entries[3] == "memtest:dir/subdir/other")
+
 debug.log("remove tree")
 file.remove_tree("memtest:dir")
 assert(not file.isdir("memtest:dir"))