def METHOD_NAME():
    class FakeSat(VectorFunction):
        center = 399
        target = None
        zero = array([0,0,0])
        def __init__(self, r):
            self.r = array(r)
        def _at(self, t):
            return self.r, self.zero, None, None
    ts = api.load.timescale()
    t = ts.utc(2023, 4, 8, 1, 25)
    # Earth's equatorial radius is around 6378 km.
    sats = [
        FakeSat([-9e5 / AU_KM, 0, 0]),  # far left of Earth
        FakeSat([-8e5 / AU_KM, 0, 0]),  # left of Earth
        FakeSat([0, 0, 0]),             # center of Earth
        FakeSat([8e5 / AU_KM, 0, 0]),   # right of Earth
        FakeSat([9e5 / AU_KM, 0, 0]),   # farther right of Earth
    ]
    verdicts = [
        (s2 - s1).at(t).is_behind_earth()
        for s1 in sats
        for s2 in sats
        if s2 is not s1
    ]
    assert verdicts == [
        False, True, True, True,  # First two fake sats can see each other.
        False, True, True, True,
        True, True, True, True,
        True, True, True, False,
        True, True, True, False,  # Last two fake sats can see each other.
    ]