For GLES all the relevant tests are open-source, under KhronosGroup/VK-GL-CTS on GitHub.
There's a small set of legacy "confidential" tests that you have to pass for GL conformance. They can't be open-sourced for legal reasons. The current CTS working group would like to get rid of them, but it's hard to justify spending time on GL these days...
You can definitely pass conformance with a driver that's horribly broken in practice. GL/ES/GLSL are huge and there are holes found in these specs all the time. And it's not like game developers read them anyway; whatever works on their test devices gets shipped.
There's a small set of legacy "confidential" tests that you have to pass for GL conformance. They can't be open-sourced for legal reasons. The current CTS working group would like to get rid of them, but it's hard to justify spending time on GL these days...
You can definitely pass conformance with a driver that's horribly broken in practice. GL/ES/GLSL are huge and there are holes found in these specs all the time. And it's not like game developers read them anyway; whatever works on their test devices gets shipped.