def env_var(self, var: str, default: Optional[str] = None) -> str:
        """The env_var() function. Return the overriden unit test environment variable named 'var'.

        If there is no unit test override, return the environment variable named 'var'.

        If there is no such environment variable set, return the default.

        If the default is None, raise an exception for an undefined variable.
        """
        if self.model.overrides and var in self.model.overrides.env_vars:
            return self.model.overrides.env_vars[var]
        else:
            return super().env_var(var, default)
The env_var() function. Return the overriden unit test environment variable named 'var'.

        If there is no unit test override, return the environment variable named 'var'.

        If there is no such environment variable set, return the default.

        If the default is None, raise an exception for an undefined variable.
        
core/dbt/context/providers.py