The phrase "almost impossible to test" is correct and usable in written English.
You can use it when discussing something that is very difficult or nearly unfeasible to evaluate or measure.
Example: "The new software's performance under extreme conditions is almost impossible to test without the right equipment."
Alternatives: "nearly untestable" or "virtually impossible to evaluate."
There are so many potential coating variants that it is almost impossible to test all the possibilities to optimise performance.
"In many instances," says James Eddison, a Year 2000 project manager at Unilever, "it is almost impossible to test embedded chips because they are in 'black box' situations.
One basic problem is that the mass, length and time scales quantum gravity theories are dealing with are so extremely small that it is almost impossible to test the different proposals.
"At that point you're almost a failure you have a theory that's almost impossible to test". Perhaps thankfully, such a particle seems somewhat unlikely from a theoretical standpoint.
This problem could be difficult to address since it is almost impossible to test the levels of all proteins in the cell.
Latent interaction variables take a lot of computational resources, making it almost impossible to test more complicated models in MPLUS (to estimate latent interaction variables, mathematical integration is necessary.
The IPP system, which has been condemned as a national scandal by prison governors, includes more than 3,000 prisoners who had already passed their tariff indicative release date: "They're only released when they can demonstrate to the Parole Board that they are a minimal risk to society, which is the present test, but in a prison cell they will find it almost impossible to satisfy that test.
The reason we didn't use the euglycemic insulin clamp technique is that it is almost impossible to perform this test in all the participants in this kind of large study population.
