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.
Definition of outpost. 1  1a : a security detachment dispatched by a main body of troops to protect it from enemy surpriseb : a military base established by treaty or agreement in another country. 2  2a : an outlying or frontier settlementb : an outlying branch or position of a main organization or group.