code: def swirl_velocity_field():
      x = np.linspace(-3.0, 3.0, 200)
      y = np.linspace(-3.0, 3.0, 100)
      X, Y = np.meshgrid(x, y)
      a = 0.1
      U = np.cos(a) * (-Y) - np.sin(a) * X
      V = np.sin(a) * (-Y) + np.cos(a) * X
      return x, y, U, V
  
file_path: matplotlib/lib/matplotlib/tests/test_streamplot.py
imports: import numpy
  from numpy.testing import assert_array_almost_equal
  import pytest
  import matplotlib.pyplot
  from matplotlib.testing.decorators import image_comparison
  import matplotlib.transforms
label_desc: Use image node_id 2 for calling a global function with example usage: swirl_velocity_field() and returns: x,  y,  U,  V