Is there a test for KRACK (devices and routers)?

Test scripts will indeed be published by the original author but are not available yet.

As stated by the author:

We have made scripts to detect whether an implementation of the 4-way handshake, group key handshake, or Fast BSS Transition (FT) handshake is vulnerable to key reinstallation attacks. These scripts will be released once we have had the time to clean up their usage instructions.

I expect the linked page to be updated once the script become available, so check it regularly.

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The author just published the scripts to test the devices and access points.

This post gives full instructions to check AP for KRACK ATTACK that support FT. http://rootsaid.com/krack-test/