from spb.backends.matplotlib import MB
class MBchild(MB):
    colorloop = ["r", "g", "b"]
plot(sin(x) / 3, sin(x) * S(2) / 3, sin(x), backend=MBchild)
# Expected:
## Plot object containing:
## [0]: cartesian line: sin(x)/3 for x over (-10.0, 10.0)
## [1]: cartesian line: 2*sin(x)/3 for x over (-10.0, 10.0)
## [2]: cartesian line: sin(x) for x over (-10.0, 10.0)