def METHOD_NAME(self):
    m = pyo.ConcreteModel()
    m.x = pyo.Var([1, 2, 3])
    expr = 2 * m.x[1] + 4 * m.x[2] * m.x[1] - m.x[1] * pyo.exp(m.x[3])
    variables = self._get_incident_variables(expr, linear_only=True)
    self.assertEqual(len(variables), 0)
    expr = 2 * m.x[1] + 2 * m.x[2] * m.x[3] + 3 * m.x[2]
    variables = self._get_incident_variables(expr, linear_only=True)
    self.assertEqual(ComponentSet(variables), ComponentSet([m.x[1]]))
    m.x[3].fix(2.5)
    expr = 2 * m.x[1] + 2 * m.x[2] * m.x[3] + 3 * m.x[2]
    variables = self._get_incident_variables(expr, linear_only=True)
    self.assertEqual(ComponentSet(variables), ComponentSet([m.x[1], m.x[2]]))