code: def test_formula_str():
      f1 = bmb.Formula("y ~ x")
      f2 = bmb.Formula("y ~ x", "sigma ~ 1", "gamma ~ x")
  
      assert str(f1) == "Formula(y ~ x)"
      assert str(f2) == "Formula(y ~ x, sigma ~ 1, gamma ~ x)"
  
file_path: bambi/tests/test_formula.py
imports: import pytest
  import bambi
label_desc: Use image node_id 5 for calling a global function with example usage: test_formula_str() without return types