The EICAR Anti-Virus Test File or EICAR test file is a computer file that was developed by the European Institute for Computer Antivirus Research (EICAR) and Computer Antivirus Research Organization (CARO), to test the response of computer antivirus (AV) programs. cit. Wikipedia
This is a harmless 68-byte file known to antivirus software and is intended to verify the operation of antivirus software.
The content of the EICAR test file contains the following string:
X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*
Files similar to EICAR are available, but they are official and therefore are not included in antivirus databases(example 1), except on an optional basis.
An example can be found at the following link: https://github.com/fire1ce/eicar-standard-antivirus-test-files