test/cli_argument_parser: notes outlining what additional tests are needed

src/test/cli_argument_parser.cpp

@@ -186,5 +186,10 @@ int main(int argc, char* argv[]) {
     //TODO add tests for invalid input
     std::cerr << "TODO: invalid input tests" << std::endl;
 
+    // test cases for invalid input:
+    //  - unknown flags, arguments (mixed with other input and standalone)
+    //  - too few, too many positional arguments (mixed with other input and standalone)
+    //  - check the produced error messages
+
     return 0;
 }