chromium/third_party/blink/web_tests/fast/canvas/no-alpha.html

<!DOCTYPE html>
<canvas id="c"></canvas>
<script type="text/javascript">
/*
  A test to make sure drawing a canvas with alpha = false works appropriately.
*/
const color = "rgba(120, 45, 200, 0.7)"; // A kind of half purple
const canvas = document.getElementById("c");
const ctx = canvas.getContext("2d", { alpha: false });
ctx.fillStyle = color;
ctx.fillRect(10, 10, 100, 100);
</script>
</html>