Application.ensure_started
You're seeing just the function
ensure_started, go back to Application module for more information.
Specs
ensure_started(app(), restart_type()) :: :ok | {:error, term()}
Ensures the given app is started.
Same as start/2 but returns :ok if the application was already
started. This is useful in scripts and in test setup, where test
applications need to be explicitly started:
:ok = Application.ensure_started(:my_test_dep)