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diff --git a/testing/web-platform/tests/webaudio/the-audio-api/the-audiobuffersourcenode-interface/active-processing.https.html b/testing/web-platform/tests/webaudio/the-audio-api/the-audiobuffersourcenode-interface/active-processing.https.html
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+++ b/testing/web-platform/tests/webaudio/the-audio-api/the-audiobuffersourcenode-interface/active-processing.https.html
@@ -0,0 +1,100 @@
+<!doctype html>
+<html>
+  <head>
+    <title>
+      Test Active Processing for AudioBufferSourceNode
+    </title>
+    <script src="/resources/testharness.js"></script>
+    <script src="/resources/testharnessreport.js"></script>
+    <script src="/webaudio/resources/audit-util.js"></script>
+    <script src="/webaudio/resources/audit.js"></script>
+  </head>
+
+  <body>
+    <script id="layout-test-code">
+      let audit = Audit.createTaskRunner();
+
+      // Arbitrary sample rate. And we only new a few blocks for rendering to
+      // see if things are working.
+      let sampleRate = 8000;
+      let renderLength = 10 * RENDER_QUANTUM_FRAMES;
+
+      // Offline context used for the tests.
+      let context;
+
+      // Number of channels for the AudioBufferSource. Fairly arbitrary, but
+      // should be more than 2.
+      let numberOfChannels = 7;
+
+      // Number of frames in the AudioBuffer.  Fairly arbitrary, but should
+      // probablybe more than one render quantum and significantly less than
+      // |renderLength|.
+      let bufferFrames = 131;
+
+      let filePath =
+          '../the-audioworklet-interface/processors/input-count-processor.js';
+
+      audit.define('Setup graph', (task, should) => {
+        context =
+            new OfflineAudioContext(numberOfChannels, renderLength, sampleRate);
+
+        should(
+            context.audioWorklet.addModule(filePath).then(() => {
+              let buffer = new AudioBuffer({
+                numberOfChannels: numberOfChannels,
+                length: bufferFrames,
+                sampleRate: context.sampleRate
+              });
+
+              src = new AudioBufferSourceNode(context, {buffer: buffer});
+              let counter = new AudioWorkletNode(context, 'counter');
+
+              src.connect(counter).connect(context.destination);
+              src.start();
+            }),
+            'AudioWorklet and graph construction')
+            .beResolved()
+            .then(() => task.done());
+      });
+
+      audit.define('verify count change', (task, should) => {
+        context.startRendering()
+            .then(renderedBuffer => {
+              let output = renderedBuffer.getChannelData(0);
+
+              // Find the first time the number of channels changes to 1.
+              let countChangeIndex = output.findIndex(x => x == 1);
+
+              // Verify that the count did change.  If it didn't there's a bug
+              // in the imploementation, or it takes longer than the render
+              // length to change.  for the latter case, increase the render
+              // length, but it can't be arbitrarily large.  The change needs to
+              // happen at some reasonable time after the source stops.
+              should(countChangeIndex >= 0, 'Number of channels changed')
+                  .beTrue();
+              should(
+                  countChangeIndex, 'Index where input channel count changed')
+                  .beLessThanOrEqualTo(renderLength);
+
+              // Verify the number of channels at the beginning matches the
+              // number of channels in the AudioBuffer.
+              should(
+                  output.slice(0, countChangeIndex),
+                  `Number of channels in input[0:${countChangeIndex - 1}]`)
+                  .beConstantValueOf(numberOfChannels);
+
+              // Verify that after the source has stopped, the number of
+              // channels is 1.
+              should(
+                  output.slice(countChangeIndex),
+                  `Number of channels in input[${countChangeIndex}:]`)
+                  .beConstantValueOf(1);
+            })
+            .then(() => task.done());
+      });
+
+      audit.run();
+    </script>
+
+  </body>
+</html>