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chromium/third_party/blink/web_tests/external/wpt/webaudio/the-audio-api/the-audioparam-interface/exponentialRamp-special-cases.html 

<!DOCTYPE html>
<title>Test exponentialRampToValueAtTime() special cases</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
promise_test(async function() {
  const bufferSize = 5;
  const sampleRate = 16384;
  const startSample = 3;
  const offset0 = 2.;
  const offset1 = -3.;
  const context = new OfflineAudioContext(1, bufferSize, sampleRate);

  const source = new ConstantSourceNode(context);
  source.start();
  // Explicit event to work around
  // https://bugzilla.mozilla.org/show_bug.cgi?id=1265393
  source.offset.setValueAtTime(offset0, 0.);
  source.offset.exponentialRampToValueAtTime(offset1, startSample/sampleRate);
  source.connect(context.destination);

  const buffer = await context.startRendering();
  assert_equals(buffer.length, bufferSize, "output buffer length");
  const output = buffer.getChannelData(0);
  for (let i = 0; i < startSample; ++i) {
    assert_equals(output[i], offset0, "initial offset at sample " + i);
  }
  for (let i = startSample; i < bufferSize; ++i) {
    assert_equals(output[i], offset1, "scheduled value at sample " + i);
  }
}, "v0 and v1 have opposite signs");

promise_test(async function() {
  const bufferSize = 4;
  const sampleRate = 16384;
  const startSample = 2;
  const offset = -2.;
  const context = new OfflineAudioContext(1, bufferSize, sampleRate);

  const source = new ConstantSourceNode(context);
  source.start();
  // Explicit event to work around
  // https://bugzilla.mozilla.org/show_bug.cgi?id=1265393
  source.offset.setValueAtTime(0, 0.);
  source.offset.exponentialRampToValueAtTime(offset, startSample/sampleRate);
  source.connect(context.destination);

  const buffer = await context.startRendering();
  assert_equals(buffer.length, bufferSize, "output buffer length");
  const output = buffer.getChannelData(0);
  for (let i = 0; i < startSample; ++i) {
    assert_equals(output[i], 0., "initial offset at sample " + i);
  }
  for (let i = startSample; i < bufferSize; ++i) {
    assert_equals(output[i], offset, "scheduled value at sample " + i);
  }
}, "v0 is zero");
</script>