This change seems good. You can add an error reference test for this. Here is an example of how to add an error reference test 7c2bbac. You just add a test file in tests/errors. In the test file, you pass a type apart from list to str.join(). You enable this test by adding it to tests/tests.toml. Then you just need to update the reference tests using ./run_tests.py -u. This will add a new reference .stderr and .json files.

Actually, I am still not checking the type of element inside the list which should be str, I checked grammar for asr but didn't get anything on how to iterate over list expression as it must be a list of str expressions. ast is getting generated perfectly but, I don't know how can I map ast nodes to asr nodes.

I did exact same thing you suggested, but CI is still failing , I must have missed something.

Try updating refs using ./run_tests.py -u and stage all and commit the updated refs.

After implementing and committing the required changes, you can do the following to test everything on your machine:

$ ./build0.sh
$ ./build1.sh
$ ./run_tests.py # if this fails, check for the failure and do ./run_tests.py -u to update refs.
$ cd integration_tests && ./run_tests.py # Here you can do `./run_tests.py -b c` to test c backend, use `-h` option to view all the available options

If everything works, then you are good to go.