human
I wrote the below code

    def get_canvas(c):
        return c.shared.ref
    cb = DummyCanvasBackend()
    c = GLContext()
    assert (c.shared.name is None)
    assert_raises(RuntimeError, get_canvas, c)
    assert_in('None    backend', repr(c.shared))
    c.shared.add_ref('test-foo', cb)
    assert (c.shared.ref is cb)
    assert_in('test-foo    backend', repr(c.shared))
    c.shared.add_ref('test-foo', cb)
    assert (len(c.shared._refs) == 2)
    cb = DummyCanvasBackend()
    gc.collect()
    assert_raises(RuntimeError, get_canvas, c)

What's a good function header?
 Here's a good function header?
assistant
#Here's a good function header.

def test_context_taking():