DummyIDP is a website you can use to test your application's SAML and SCIM support end-to-end. From your application's perspective, it's exactly like the identity provider ("IDP") your customers use, but unlike commercial IDPs there's no "input your email" or "talk to sales" step to use DummyIDP.
DummyIDP implements the "Identity Provider" side of the SAML and SCIM protocols. It is meant for use as a way to test your application's support for the "Service Provider" side of the SAML and SCIM protocols. See "DummyIDP Security Posture" for details.