public abstract @NonNull VirtualFile[] list() throws IOException;
@Test
    public void simpleList_NoKids_AbstractBase() throws Exception {
        // This test checks the method's behavior in the abstract base class,
        // which generally does nothing.
        File root = tmp.getRoot();
        FileUtils.touch(root);
        VirtualFile virtualRoot = new VirtualFileMinimalImplementation(root);
        List<VirtualFile> children = Arrays.asList(virtualRoot.list());
        assertThat(children, empty());
    }