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One test by anyone does not give an absolute indicator of reliability. Funny that you praise John’s test of one scope, and with the next sentence denigrate Form’s test of one scope.

Having said that, a single test that reveals a failure is far more telling than a single test that shows no failure. Here’s why: if it were possible to thoroughly test every scope of a given model, we may notice a trend of one failure in 100 scopes, for example. If we test one scope from this batch we expect to see no failure, as the probability of the scope passing the test is 99 in 100. Another model of scope may have a failure rate of 1 in 10. If we put all the scopes of both models in a pile and randomly test two scopes, with neither showing a failure, we don’t know whether we are testing the scope with one failure in 10, or one in 100. But if our random two tests both show scope failures, it becomes much more likely that we are testing a scope with a high failure rate, due to the likelihood of randomly getting a failure. A scope test that leads to failure says a lot more about the scope then a test showing a scope working the way it supposed to.