Here are two ways to generate the IDF using the OpenStudio CLI without running a simulation:

1. Use an OpenStudio Workflow (OSW)

Create a file called test.osw with the following contents:

{
  "seed_file": "test.osm"
}

Then run openstudio run -m -w test.osw, where the -m flag prevents the simulation from running. You will find the IDF at run/in.idf.

2. Use the OpenStudio SDK

Create a simple ruby script called generate_idf.rb with the following contents:

vt = OpenStudio::OSVersion::VersionTranslator.new
model = vt.loadModel(OpenStudio::Path.new("test.osm")).get
ft = OpenStudio::EnergyPlus::ForwardTranslator.new
model_idf = ft.translateModel(model)
File.open("test.idf", "w") { |f| f << model_idf.to_s }

Then run openstudio generate_idf.rb. It will create a test.idf file next to your test.osm file.