Litmus test: 
Carboxylic acid turn blue litmus red.

Sodium bicarbonate test:
Evolution of carbon dioxide with brisk effervescence on adding sodium bicarbonate shows the presence of carboxylic acid.

Ester test:
The compound to be tested is warmed with small quantity of ethyl alcohol and 2-3 drops of concentrated sulphuric acid. The formation of sweet smelling vapours indicates the presences of some carboxylic acid.
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oh i see!
by then !
: )
: )