code: def test_as_explicit():
      c0, c1, c2 = symbols("c0:3")
      x = Symbol("x")
      assert CompanionMatrix(
          Poly([1, c0], x)
      ).as_explicit() == ImmutableDenseMatrix([-c0])
      assert CompanionMatrix(
          Poly([1, c1, c0], x)
      ).as_explicit() == ImmutableDenseMatrix([[0, -c0], [1, -c1]])
      assert CompanionMatrix(
          Poly([1, c2, c1, c0], x)
      ).as_explicit() == ImmutableDenseMatrix(
          [[0, 0, -c0], [1, 0, -c1], [0, 1, -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 4 for calling a global function with example usage: test_as_explicit() without return types