The phrase "a difficult test for" is correct and usable in written English.
It can be used when describing a challenge or assessment that is particularly hard for someone or something.
Example: "The exam was a difficult test for the students, pushing them to their limits."
Alternatives: "a challenging assessment for" or "a tough evaluation for".
It could be a difficult test for Kentucky, which has won at least one tournament game every year since 1987.
The state is expecting a deficit next year of at least $7 billion, setting up a difficult test for the next governor.
In recent months, dozens of foreigners have been kidnapped in Iraq, posing a difficult test for nations that have sent troops to Iraq or who have nationals working here.
Taking charge after a lightning-fast transition will be a difficult test for Mr. Paterson, who is liked and respected by leading figures in both parties, but relatively new to statewide office.
Numerical applications are performed using as working examples steel concrete two-span continuous beams, a problem of practical interest in structural engineering and a difficult test for composite beam elements.
The events in the Middle East have proven a difficult test for Mitt Romney in particular; he's been criticized, including by some in his own party, for the way he attacked the Obama Administration in the wake of the incidents in Benghazi and Cairo.
Ethiopia presents a particularly difficult test for climate models.
"It's going to be a very difficult test for us but we're going into the game with confidence.
This led from Greenland to Ellesmere Island and proved a difficult test, largely across pack-ice, for men and equipment.
It is a difficult test in the early going for the new speaker, who remains largely unfamiliar to most Americans.
Researchers discovered that subjects spent more time studying for a difficult test following an initial failure when they practiced self-compassion.
