tests/printf: Fix char_as_byte test, add char and string padding tests

tests/by-util/test_printf.rs

@@ -673,7 +673,11 @@ fn sub_alternative_upper_hex() {
 
 #[test]
 fn char_as_byte() {
-    new_ucmd!().args(&["%c", "🙃"]).succeeds().stdout_only("ð");
+    new_ucmd!()
+        .args(&["%c", "🙃"])
+        .succeeds()
+        .no_stderr()
+        .stdout_is_bytes(b"\xf0");
 }
 
 #[test]
@@ -736,3 +740,34 @@ fn pad_unsigned_three() {
             .stdout_only(expected);
     }
 }
+
+#[test]
+fn pad_char() {
+    for (format, expected) in [
+       ("%3c", "  X"),
+       ("%1c", "X"),
+       ("%-1c", "X"),
+       ("%-3c", "X  "),
+    ] {
+        new_ucmd!()
+            .args(&[format, "X"])
+            .succeeds()
+            .stdout_only(expected);
+    }
+}
+
+
+#[test]
+fn pad_string() {
+    for (format, expected) in [
+       ("%8s", "  bottle"),
+       ("%-8s", "bottle  "),
+       ("%6s", "bottle"),
+       ("%-6s", "bottle"),
+    ] {
+        new_ucmd!()
+            .args(&[format, "bottle"])
+            .succeeds()
+            .stdout_only(expected);
+    }
+}