ex);

    shouldBeNull("gl.getTexParameter(gl.TEXTURE_2D, 0x90EA /* DEPTH_STENCIL_TEXTURE_MODE_WEBGL */)");
    wtu.glErrorShouldBe(gl, gl.INVALID_ENUM, "parameter unknown without enabling the extension");
    wtu.glErrorShouldBe(gl, gl.NO_ERROR, "should be no more errors");

    gl.texParameteri(gl.TEXTURE_2D, 0x90EA /* DEPTH_STENCIL_TEXTURE_MODE_WEBGL */, gl.DEPTH_COMPONENT);
    wtu.glErrorShouldBe(gl, gl.INVALID_ENUM, "parameter unknown for texParameteri without enabling the extension");
    wtu.glError