setup

test atan2( 0,  1) is 0
test atan2( 1,  1) is pi / 4
test atan2( 1,  0) is pi / 2
test atan2( 1, -1) is 3 * pi / 4
test atan2( 0, -1) is pi
test atan2(-1, -1) is -3 * pi / 4
test atan2(-1,  0) is -pi / 2
test atan2(-1,  1) is -pi / 4

teardown