According to Jon Leech (EGL & OpenGL Specification Editor / OpenGL ARB Ecosystem TSG Chair / Khronos API RegistrarEGL)
There is some minimal coverage testing in the client API-specific tests, and the OpenKODE tests address use of multiple client APIs together, to a limited degree. It's pretty hard to test EGL in isolation since it really doesn't do anything without a client API to operate on the resources it manages