A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

Note: 
The expression does not correlate in meaning with the
phrase tent camper—
1
. a campsite dweller: There will be a quiet
area for tent campers who want to go to sleep after the evening
performances have ended. 2. a trailer vehicle furnished for
camping: So my husband and I rented a tent camper for the
weekend. We loved it!
test bed • tester bed
test bed —equipment for testing engines, etc. before their
acceptance for general use: Once the engine was finished it
was tested on a test bed, outside of the car it would be built
into.
tester bed —a bed with four corner posts and a canopy: We
continued in this suburb three days, during the greatest part
of which time I was stretched on the tester bed.
test someone for something • test someone on
something
test someone for something —perform a medical check on a
person to detect a possible disease, etc.: The doctors tested
him for malaria and other illnesses.
test someone on something —ask questions to find out how
much a person knows about a subject: The teacher tested me
on my knowledge of French.
that makes two of us • two can play at that game
that makes two of us —
1
. is used to say that one is in the
same position: She wanted reassurance. That makes two of
us, he thought. 2. is used to indicate agreement with what
another speaker just said: “I find the Church’s stance in this
case absolutely revolting.” “That makes two of us, Chris.” Cf.:
that makes one of us — my opinion is different from yours here
(used as a pun on the former): “Liz, I’m really glad you decided
to come here,” I said. She gave a short laugh. “So far that
makes one of us.”
two can play at that game —is used to say that one can act
in a similar objectionable way (as retaliation for smb.’s unfair
practices): Sulking until you get your own way is a game that
two can play, you know.