code: def check_constant_output(self, expr, expected):
      self.assertFalse(isnan(expected))
      return self.check_output(expr, full((5, 5), expected, float))
  
imports: from itertools import permutations
  from operator import add, ge, gt, le, lt, methodcaller, mul, ne, sub
  from string import ascii_uppercase
  from unittest import TestCase
  import numpy
  from numpy import arange, array, eye, float64, full, isnan, zeros
  from pandas import DataFrame, date_range, Int64Index
  from catalyst.pipeline import Factor, Filter
  from catalyst.pipeline.expression import NumericalExpression, NUMEXPR_MATH_FUNCS
  from catalyst.testing import check_allclose
  from catalyst.utils.numpy_utils import datetime64ns_dtype, float64_dtype
label_desc: Use image node_id 3 for calling the NumericalExpressionTestCase obj's underlying member method code with example usage: obj.check_constant_output(expr, expected) and returns: self