d so clearing should clear a 2x2 area
// and calling read pixels should read the clear color in that 2x2 area
// and 0,0,0,0 outside that area.
//
// If the FBO is no longer bound because of a WebGL implementation error
// then likely the clear will clear the backbuffer and reading outside
// the 2x2 area will not be 0,0,0,0

function test() {
  gl.clearColor(0, 0, 1, 1);
  gl.clear(gl.COLOR_BUFFER_BIT);
  checkFBO(blue, "should be blue");
  gl.clearColor(0, 1, 0, 1);
  gl.clear(gl.COLOR_BUFFER_BIT);
  chec