code: def test_sigmoid_expr():
      expr = ast.SigmoidExpr(ast.NumVal(2.0))
  
      expected_code = """
  using static System.Math;
  namespace ML {
      public static class Model {
          public static double Score(double[] input) {
              return Sigmoid(2.0);
          }
          private static double Sigmoid(double x) {
              if (x < 0.0) {
                  double z = Exp(x);
                  return z / (1.0 + z);
              }
              return 1.0 / (1.0 + Exp(-x));
          }
      }
  }
  """
  
      interpreter = CSharpInterpreter()
      assert_code_equal(interpreter.interpret(expr), expected_code)
  
imports: from itertools import product
  import pytest
  from m2cgen import ast
  from m2cgen.interpreters import CSharpInterpreter
  from tests.utils import assert_code_equal
label_desc: Use image node_id 21 for calling a global function with example usage: test_sigmoid_expr() without return types