test: add parse line single word test

src/parse.rs

@@ -9,3 +9,13 @@ pub fn parse_line(line: &str) -> Result<(&str, Vec<String>), ShellError> {
         Err(ShellError::MalformedArgs(unparsed_args.to_string()))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse_single() {
+        assert_eq!(parse_line("keyword"), Ok(("keyword", vec![])))
+    }
+}