from spb import multiples_of_pi_over_2, multiples_of_pi_over_3
expr = 5 * (cos(x) - 0.2 * sin(y))**2 + 5 * (-0.2 * cos(x) + sin(y))**2
plot_contour(
    expr, (x, 0, 2 * pi), (y, 0, 2 * pi),
    x_ticks_formatter=multiples_of_pi_over_2(),
    y_ticks_formatter=multiples_of_pi_over_3(),
    is_filled=False
)
# Expected:
## Plot object containing:
## [0]: contour: 5*(-0.2*sin(y) + cos(x))**2 + 5*(sin(y) - 0.2*cos(x))**2 for x over (0, 2*pi) and y over (0, 2*pi)