code: def test_simple_f_header():
      x, y, z = symbols("x,y,z")
      expr = (x + y) * z
      routine = make_routine("test", expr)
      code_gen = FCodeGen()
      source = get_string(code_gen.dump_h, [routine])
      expected = (
          "interface\n"
          "REAL*8 function test(x, y, z)\n"
          "implicit none\n"
          "REAL*8, intent(in) :: x\n"
          "REAL*8, intent(in) :: y\n"
          "REAL*8, intent(in) :: z\n"
          "end function\n"
          "end interface\n"
      )
      assert source == expected
  
imports: from io import StringIO
  from sympy.core import symbols, Eq, pi, Catalan, Lambda, Dummy
  from sympy.core.relational import Equality
  from sympy.core.symbol import Symbol
  from sympy.functions.special.error_functions import erf
  from sympy.integrals.integrals import Integral
  from sympy.matrices import Matrix, MatrixSymbol
  from sympy.utilities.codegen import codegen, make_routine, CCodeGen, C89CodeGen, C99CodeGen, InputArgument, CodeGenError, FCodeGen, CodeGenArgumentListError, OutputArgument, InOutArgument
  from sympy.testing.pytest import raises
  from sympy.utilities.lambdify import implemented_function
label_desc: Use image node_id 35 for calling a global function with example usage: test_simple_f_header() without return types