r, theta = symbols("r, theta")
plot_contour(sin(2 * r) * cos(theta), (theta, 0, 2*pi), (r, 0, 7),
    {"levels": 100}, polar_axis=True, aspect="equal")
# Expected:
## Plot object containing:
## [0]: contour: sin(2*r)*cos(theta) for theta over (0, 2*pi) and r over (0, 7)