Add test coverage for der.rs

src/der.rs

@@ -211,5 +211,38 @@ mod tests {
     }
 
     #[test]
-    fn test_bit_string_with_no_unused_bits() {}
+    fn test_bit_string_with_no_unused_bits() {
+        use super::{bit_string_with_no_unused_bits, Error};
+
+        // Unexpected type
+        assert_eq!(
+            Err(Error::BadDer),
+            bit_string_with_no_unused_bits(&mut bytes_reader(&[0x01, 0x01, 0xff]))
+        );
+
+        // Unexpected nonexistent type
+        assert_eq!(
+            Err(Error::BadDer),
+            bit_string_with_no_unused_bits(&mut bytes_reader(&[0x42, 0xff, 0xff]))
+        );
+
+        // Unexpected empty input
+        assert_eq!(
+            Err(Error::BadDer),
+            bit_string_with_no_unused_bits(&mut bytes_reader(&[]))
+        );
+
+        // Valid input with non-zero unused bits
+        assert_eq!(
+            Err(Error::BadDer),
+            bit_string_with_no_unused_bits(&mut bytes_reader(&[0x03, 0x03, 0x04, 0x12, 0x34]))
+        );
+
+        // Valid input
+        assert_eq!(
+            untrusted::Input::from(&[0x12, 0x34]),
+            bit_string_with_no_unused_bits(&mut bytes_reader(&[0x03, 0x03, 0x00, 0x12, 0x34])).unwrap()
+        );
+    }
 }
+