How to provide parameters for test node in launch testing using yaml file file

edit

I was able to read by using the basic python read file function for reading the YAML file and then converting it to the dictionary and then using it to read the required parameter.
This issue I mentioned is for launch testing only. For regular nodes giving parameters from launch, the file works perfectly.
I am not sure if this is the right way to do it but it seems like the easiest way to do it. If anyone still has a better idea or way please share it.

Updated my solution using @ljaniec recommendation.

Below is an example of how I solved it.

config_path = os.path.join(get_package_share_directory('pkg_name'), 'config/params.yaml')
with open(config_path) as stream:
    data_dict = yaml.load(stream, Loader = yaml.SafeLoader)
    robot_name = data_dict['test_node']['ros__parameters']['robot_name']
    spin_time = int(data_dict['test_node']['ros__parameters']['test_spin_time'])