Q:

Is it possible to connect Shibboleth idp from localhost?

I installed Shibboleth service provider on localhost. I want to connect to shibboleth idp. 

Error Message: No peer endpoint available to which to send SAML response

This is because I connect to IDP(idp.shibtest.org) from localhost?

A:

testshib.org is good way to test shibboleth.
You cannot use localhost as SP to connect to remote IDp, that iDp won't find any SP to return to because localhost means it's own system so IDp would go in it's local system and find your given SP's entity ID. It won't find that entity ID so it would give such error.
These two approach may help you

Give your machine some public IP and try connect to IDp with that SP.
If you cannot make public IP, make both SP and IDp in your local system.
My this answer may help you.

