du: add test for -d flag

tests/fixtures/du/subdir/links/subwords2.txt

@@ -0,0 +1 @@
+hello

tests/fixtures/du/words.txt

@@ -1 +1 @@
-hello
+hi

tests/test_du.rs

@@ -1,18 +1,22 @@
 use common::util::*;
-use std::fs::set_permissions;
 
-static SUB_DIR: &str = "subdir";
-static SUB_FILE: &str = "subdir/subwords.txt";
-static SUB_LINK: &str = "subdir/sublink.txt";
+static SUB_DIR: &str = "subdir/deeper";
+static SUB_DIR_LINKS: &str = "subdir/links";
+static SUB_FILE: &str = "subdir/links/subwords.txt";
+static SUB_LINK: &str = "subdir/links/sublink.txt";
 
 #[test]
 fn test_du_basics() {
     let (_at, mut ucmd) = at_and_ucmd!();
-
+    let answer = "32\t./subdir
+8\t./subdir/deeper
+24\t./subdir/links
+40\t./
+";
     let result = ucmd.run();
     assert!(result.success);
     assert_eq!(result.stderr, "");
-    assert_eq!(result.stdout, "24\t./subdir\n32\t./\n");
+    assert_eq!(result.stdout, answer);
 }
 
 #[test]
@@ -22,7 +26,7 @@ fn test_du_basics_subdir() {
     let result = ucmd.arg(SUB_DIR).run();
     assert!(result.success);
     assert_eq!(result.stderr, "");
-    assert_eq!(result.stdout, "24\tsubdir\n");
+    assert_eq!(result.stdout, "8\tsubdir/deeper\n");
 }
 
 #[test]
@@ -41,10 +45,10 @@ fn test_du_soft_link() {
     let link = ts.cmd("ln").arg("-s").arg(SUB_FILE).arg(SUB_LINK).run();
     assert!(link.success);
 
-    let result = ts.ucmd().arg(SUB_DIR).run();
+    let result = ts.ucmd().arg(SUB_DIR_LINKS).run();
     assert!(result.success);
     assert_eq!(result.stderr, "");
-    assert_eq!(result.stdout, "32\tsubdir\n");
+    assert_eq!(result.stdout, "32\tsubdir/links\n");
 }
 
 #[test]
@@ -54,21 +58,19 @@ fn test_du_hard_link() {
     let link = ts.cmd("ln").arg(SUB_FILE).arg(SUB_LINK).run();
     assert!(link.success);
 
-    let result = ts.ucmd().arg(SUB_DIR).run();
+    let result = ts.ucmd().arg(SUB_DIR_LINKS).run();
     assert!(result.success);
     assert_eq!(result.stderr, "");
     // We do not double count hard links as the inodes are identicle
-    assert_eq!(result.stdout, "24\tsubdir\n");
+    assert_eq!(result.stdout, "24\tsubdir/links\n");
 }
 
-// todo:
-// du on file with no permissions
-// du on multi dir with '-d'
-//
-/*
- * let mut permissions = at.make_file(TEST_HELLO_WORLD_DEST)
- * .metadata()
- * .unwrap()
- * .permissions();
- * permissions.set_readonly(true);
- */
+#[test]
+fn test_du_d_flag() {
+    let ts = TestScenario::new("du");
+
+    let result = ts.ucmd().arg("-d").arg("1").run();
+    assert!(result.success);
+    assert_eq!(result.stderr, "");
+    assert_eq!(result.stdout, "32\t./subdir\n40\t./\n");
+}