Naturally the first complaint will come from applicants: we will have to pay for building the object we want a monopoly on? That's expensive! It takes a long time! It might not work!
Having been on the other side - developing products that take a lot of money and a long time, and might not work - for the last few decades, I don't have a lot of sympathy for this position. As we noted previously, only about 10% of US applications these days are owned by individuals, the remainder being assigned to corporations or other organizations. Corporate filers who are filing to protect their product line have the resources to build what they patent. Corporate filers who don't are probably Non-Practicing Entities (trolls), and should be expunged from the system in any case. Individual filers who don't have the resources to practice the invention they claim to have conceived can't demonstrate that they've actually enabled anyone else to do so. In effect, they are now required to find a partner with sufficient resources - which they needed to do anyway to get anything out of their patent, unless their strategy was to sue people who have independently developed what they claim to own, a reprehensible position society need not support.
A more serious objection is raised when one asks how to actually proceed with a test. Many real products require access to specialized resources, in some cases not easily reproduced. For example, an application dealing with semiconductor processing (the techniques used to make an integrated circuit wafer) may require modifications to a process step. Semiconductor fabrication factories ("fabs") cost hundreds of millions of dollars to set up and more millions to run, and do not make modifications to their processes for one customer, as this can put other customer's products at risk. An applicant who is an employee of such a fab may have the ability to test enablement - but they already know what the invention is and can't test obviousness. And if the test is conducted in the applicant's facility, they can provide numerous resources for enablement that are not disclosed in the application and not available to skilled people elsewhere, allowing them to appear to pass the test while not disclosing important information. Similarly, an algorithm might require specialized code libraries that are not publicly available; a drug might need unique catalysts or analytical capabilities.
But the problem here is more apparent than real. The false assumption that everyone ought to be granted monopolies, in the absence of any demonstration that they are deserved, is the difficulty. The result of imposing an empirical test requirement in the above circumstances is that filings cannot be made for ideas whose practicality cannot be demonstrated without an applicant's specialized resources. In business terms, we have just defined the situation where competitive advantage is mainly obtained from internally-developed or acquired resources not readily available to competitors or the public. Rights to exclude are irrelevant to the business and thus not needed by society. Typically such resources become available with the passing of time (and the competitive advantage of early vertically-integrated players is eroded). Empirical testing becomes possible just when it becomes necessary.
A more fundamental challenge is to ensure that both obviousness and enablement tests are not contaminated by the applicants. Testing should ideally proceed using resources that are independent from those available in the applicant's organization, and with no personal contact between the applicants or their representatives and the people performing the test. Further, the folks performing the tests should be able to act independently of their client's perceived interest. In the iterated-prisoner's-dilemma world of real business, where people deal with each other repeatedly, a firm may be tempted to always be stupid about invention and brilliant about enablement. The only way to avoid this result is to allow both applicants and competitors to fund the tests, and forbid their identity to be revealed. In this case, the performing person or firm doesn't know which side they are working for, and thus has no incentive to taint the results.
Another subtle issue is that in the event that the test is performed when the relevant patent application has been published, how are the testers to be prevented from accessing the application or patent during the obviousness test, while still having access to other relevant art? It seems necessary to implement a search engine that excludes the patent or application under examination, and any continuations  thereof. That's not very hard. However, the persons performing the test must agree to avoid the use of general-purpose patent search engines, so they don't get the patent before they are supposed to. That's harder: now we're dealing with human nature rather than code. A successful implementation will require procedures that do not impede research but also don't give away the answer, and the procedures may work better in some areas of art than in others. It's also possible the procedures will be different for e.g. a drug for human consumption and an embedded software program.
Finally, even if the testing is conducted in an ethical and thoughtful fashion, the results may be unintelligible, not just to a lay jury and judge but even to experts in the field. Engineers generally don't write well. That's why you probably need the people involved to provide testimony, so that the mysterious parts have some hope of explanation. (Not that a deposition is the best environment to get clarity - but it's what we've got.)
We can conclude that considerable thought, and some experimentation, will be needed to produce a useful implementation of empirical testing. And that's in addition to the need for legislation and international agreements. I told you it would get harder, not easier, as we progressed.
The great benefit of empirical testing is the stripping out of crap. In the absence of reference to experiment, human activities become the proverbial counting-angels-on-the-head-of-a-pin silliness. That's what the modern patent system is. Testing exposes plausible but false assertions in a system whose assumptions are today never challenged. Instead of unending silly arguments about what is obvious and what isn't, we have a factual examination of whether a bunch of folks came up with the "invention" after ten minutes of brainstorming, or worked for six months and never thought of anything like it. Instead of trivializing the hard part of innovation - getting an idea to actually work - we see if the supposed revelations of the specification produce a working model or a catastrophe. Litigation will still be an exercise in rationalization, but at least judge and jury will have anchors in reality they can use to constrain the fantasies of the competing parties.
The requirement for testing will also greatly reduce the number of granted patents that are likely to be the subjects of litigation. Most patents will simply be abandoned as not worth testing. Many others will be found obvious in testing, or fail enablement, causing their owners to abandon the patent, or at least to avoid litigating with it.
A secondary if narrower benefit is an opportunity for useful employment for people in any field in which patents are sought. As an engineer, I am, of course, lobbying for my folks here, though if the regime of applicability of patents continues to increase, other groups benefit, too. Why should the system only employ attorneys and patent agents? An empirical test regime would create an opportunity for people and consulting firms to make a living while (hopefully) adding value for society.
Finally, in making public the results of development work funded by would-be monopolists, we do what the system is supposed to do but often doesn't: we show folks exactly how to practice the supposed invention, and thus ensure that an invention that is enabled actually adds to our knowledge of how to do useful things.
And that's only the second-most insanely audacious proposal. More next time.
1: A continuation is a patent application that uses the same specification as an earlier application, but has a different set of claims. A continuation-in-part adds new material to an earlier specification, and has additional claims.