 gl.samplerParameteri(sampler, gl[pname], MIRROR_CLAMP_TO_EDGE_EXT);
        wtu.glErrorShouldBe(gl, gl.INVALID_ENUM, `value unknown for ${pname} via samplerParameteri without enabling the extension`);
        wtu.glErrorShouldBe(gl, gl.NO_ERROR, "should be no more errors");
        gl.samplerParameterf(sampler, gl[pname], MIRROR_CLAMP_TO_EDGE_EXT);
        wtu.glErrorShouldBe(gl, gl.INVALID_ENUM, `value unknown for ${pname} via samplerParameterf without enabling the extension`);
        wtu.glErrorShouldBe