Sperm penetration tests check to see whether a man's sperm can move through cervical mucus and the fallopian tubes to join with (fertilize) an egg. This test is usually done when a couple is having trouble becoming pregnant (infertility). There are different sperm penetration tests.
The idea that a boundary is shifting can be applied to different areas. A shifting frontier of science would be referring to the fact that science is always changing and growing, and always with new areas. In wartime, a shifting frontier would be an international border which is constantly being renegotiated.
frontier c.1400, from O.Fr. fronter, from front brow (see front). Originally the front line of an army, sense of borderland is first attested 1413. In reference to N.Amer., from 1676; later with a specific sense:What is the frontier? ... In the census reports it is treated as the margin of that settlement which has a density of two or more to the square mile. [F.J. Turner, The Frontier in American History]Frontiersman is from 1782.