On January 9, the Illinois legislature passed a bill for a special statewide election in November 2016 for Comptroller. The outgoing Governor, Pat Quinn, has already asked for this bill, so it seems certain he will sign it before he leaves office.
This will mean three statewide offices will be on the November 2016 ballot in Illinois: President, U.S. Senator, and Comptroller. Any party that polls 5% for any of them will be automatically on the 2018 ballot for statewide office only.
Since it is styled a special election, albeit coincident with a general election, it is not clear that the vote test applies.
I checked the Illinois law and it does not exclude special elections. It says “A political party which, at the last general election for State and county officers, polled more than 5% of the entire vote cast, is hereby declared to be an ‘established political party.'” November 2016 is a general election for State and county officers. If the bill required the special election to be at a time when no other office was on the ballot, then you would be right.
There is ambiguity there. While it does not exclude special elections, it does not include them either.
In Texas, a special election held on the date of a general election does not have partisan nominations, and the straight ticket device does not apply. So that race could not be used for party qualification.
If a court were trying to determine legislative intent, the court might well conclude that the Illinois legislature would never do anything intentionally to facilitate ballot access.