diff --git a/src/builtins/ls.rs b/src/builtins/ls.rs
index 48456ae..63beb84 100644
--- a/src/builtins/ls.rs
+++ b/src/builtins/ls.rs
@@ -103,3 +103,13 @@ fn right_padding(s: &str, max: usize) -> String {
     }
     tmp
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_format_filesize_bytes() {
+        assert_eq!(format_filesize(6969), "6969B");
+    }
+}