def METHOD_NAME(self, compare_lps):
    self.TEST_REGISTER.add("variables.energy_cap")
    model = build_test_model(
        {
            "nodes.b.techs.test_supply_elec.constraints.energy_cap_max": 100,
            "nodes.a.techs.test_supply_elec.constraints.energy_cap_min": 1,
            "nodes.a.techs.test_supply_elec.constraints.energy_cap_max": np.nan,
        },
        "simple_supply,two_hours,investment_costs",
    )
    custom_math = {
        # need the variable defined in a constraint/objective for it to appear in the LP file bounds
        "objectives": {
            "foo": {
                "equations": [
                    {
                        "expression": "sum(energy_cap[techs=test_supply_elec], over=nodes)"
                    }
                ],
                "sense": "minimise",
            }
        }
    }
    compare_lps(model, custom_math, "energy_cap")
    # "energy_cap" is the name of the lp file