code: def test_subs():
      assert s1.subs(s1, s2) == s2
      assert v1.subs(v1, v2) == v2
      assert f1.subs(f1, f2) == f2
      assert (x * f(s1) + y).subs(s1, s2) == x * f(s2) + y
      assert (f(s1) * v1).subs(v1, v2) == f(s1) * v2
      assert (y * f(s1) * f1).subs(f1, f2) == y * f(s1) * f2
  
imports: from sympy.diffgeom import Manifold, Patch, CoordSystem, Point
  from sympy.core.function import Function
  from sympy.core.symbol import symbols
  from sympy.testing.pytest import warns_deprecated_sympy
label_desc: Use image node_id 2 for calling a global function with example usage: test_subs() without return types