There are, I think, two reasons why that example is OK. First, it's from a newspaper. The combination of present perfect with a time in the past is sometimes found in journalistic style.
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what is missing from the sentence "The U.S. military has conducted tests in the past" is a very definite likehood it will be followed with more consolidating sentence information that will give more detail to the one sentence in questionCould you give an example of a "more consolidating sentence information" that might follow "The U.S. military has conducted tests