tests: add test for d0

Test to stop bug in previous commit occuring
Also cargo clippy

src/filter.rs

@@ -32,8 +32,7 @@ pub fn get_biggest(
 
     if number_top_level_nodes == 0 {
         root = total_node_builder(0, vec![])
-    } else {
-        if number_top_level_nodes > 1 {
+    } else if number_top_level_nodes > 1 {
         let size = if by_filetime.is_some() {
             top_level_nodes
                 .iter()
@@ -46,9 +45,9 @@ pub fn get_biggest(
 
         let nodes = handle_duplicate_top_level_names(top_level_nodes, display_data.short_paths);
         root = total_node_builder(size, nodes);
+        heap = always_add_children(&display_data, &root, heap);
     } else {
         root = top_level_nodes.into_iter().next().unwrap();
-        }
         heap = add_children(&display_data, &root, heap);
     }
 

tests/test_flags.rs

@@ -62,6 +62,14 @@ pub fn test_d_flag_works() {
     assert!(!output.contains("hello_file"));
 }
 
+#[test]
+pub fn test_d0_works_on_multiple() {
+    // We should see the top level directory but not the sub dirs / files:
+    let output = build_command(vec!["-d", "0", "tests/test_dir/", "tests/test_dir2"]);
+    assert!(output.contains("test_dir "));
+    assert!(output.contains("test_dir2"));
+}
+
 #[test]
 pub fn test_threads_flag_works() {
     let output = build_command(vec!["-T", "1", "tests/test_dir/"]);