The adopter program lets potential adoptees run the OpenGL ES 3.1 conformance test for possible certification as their driver's implementation being conformant to the official specification. The ES 3.1 test is obviously built atop the existing OpenGL ES 3.0 test.
Mentioned at Khronos.org, "It adds eighteen new test categories covering the new features of ES 3.1, including compute shaders, image and buffer object load/store, atomic operations, and indirect drawing. In addition to the conformance test, the working group has released updated API and shading language specifications, containing many corrections and clarifications."
Intel's open-source Linux crew has already published a set of 15 patches to correct their Mesa driver against these OpenGL ES 3 conformance tests. Intel does invest the time and resources for OpenGL ES certification of their Linux stack while the other open-source drivers haven't done so for official certification.