code: def test_entry():
      c0, c1, c2 = symbols("c0:3")
      x = Symbol("x")
      A = CompanionMatrix(Poly([1, c2, c1, c0], x))
      assert A[0, 0] == 0
      assert A[1, 0] == 1
      assert A[1, 1] == 0
      assert A[2, 1] == 1
      assert A[0, 2] == -c0
      assert A[1, 2] == -c1
      assert A[2, 2] == -c2
  
file_path: sympy/sympy/matrices/expressions/tests/test_companion.py
imports: from sympy.core.expr import unchanged
  from sympy.core.symbol import Symbol, symbols
  from sympy.matrices.immutable import ImmutableDenseMatrix
  from sympy.matrices.expressions.companion import CompanionMatrix
  from sympy.polys.polytools import Poly
  from sympy.testing.pytest import raises
label_desc: Use image node_id 3 for calling a global function with example usage: test_entry() without return types