Final answer:
Competitive interference with test-marketing is known as predatory pricing, a tactic to deter competition and create barriers to entry that is illegal under U.S. antitrust law but hard to prove.
Step-by-step explanation:
Competitive interference with a test-marketing program is referred to as predatory pricing, which is a strategic maneuver employed by businesses to establish barriers to entry and deter competition. This aggressive tactic involves the threat of significant price reductions that can undermine the stability of competitors who are either in the market or considering entry. While predatory pricing can provide a temporary advantage to the firm utilizing it, it is regarded as anti-competitive behavior and is a violation of U.S. antitrust law, although it can be challenging to prove in a court of law.