Import wpt@503f5b5f78ec4e87d144f78609f363f0ed0ea8db

third_party/WebKit/LayoutTests/external/wpt/streams/writable-streams/floating-point-total-queue-size.js

Index: third_party/WebKit/LayoutTests/external/wpt/streams/writable-streams/floating-point-total-queue-size.js
diff --git a/third_party/WebKit/LayoutTests/external/wpt/streams/writable-streams/floating-point-total-queue-size.js b/third_party/WebKit/LayoutTests/external/wpt/streams/writable-streams/floating-point-total-queue-size.js
new file mode 100644
index 0000000000000000000000000000000000000000..44cf5fb22fd32107758f2f6e480d57ac31848c0c
--- /dev/null
+++ b/third_party/WebKit/LayoutTests/external/wpt/streams/writable-streams/floating-point-total-queue-size.js
@@ -0,0 +1,90 @@
+'use strict';
+
+if (self.importScripts) {
+  self.importScripts('/resources/testharness.js');
+}
+
+// Due to the limitations of floating-point precision, the calculation of desiredSize sometimes gives different answers
+// than adding up the items in the queue would. It is important that implementations give the same result in these edge
+// cases so that developers do not come to depend on non-standard behaviour. See
+// https://github.com/whatwg/streams/issues/582 and linked issues for further discussion.
+
+promise_test(() => {
+  const writer = setupTestStream();
+
+  const writePromises = [
+    writer.write(2),
+    writer.write(Number.MAX_SAFE_INTEGER)
+  ];
+
+  assert_equals(writer.desiredSize, 0 - 2 - Number.MAX_SAFE_INTEGER,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (after writing two chunks)');
+
+  return Promise.all(writePromises).then(() => {
+    assert_equals(writer.desiredSize, 0, '[[queueTotalSize]] must clamp to 0 if it becomes negative');
+  });
+}, 'Floating point arithmetic must manifest near NUMBER.MAX_SAFE_INTEGER (total ends up positive)');
+
+promise_test(() => {
+  const writer = setupTestStream();
+
+  const writePromises = [
+    writer.write(1e-16),
+    writer.write(1)
+  ];
+
+  assert_equals(writer.desiredSize, 0 - 1e-16 - 1,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (after writing two chunks)');
+
+  return Promise.all(writePromises).then(() => {
+    assert_equals(writer.desiredSize, 0, '[[queueTotalSize]] must clamp to 0 if it becomes negative');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up positive, but clamped)');
+
+promise_test(() => {
+  const writer = setupTestStream();
+
+  const writePromises = [
+    writer.write(1e-16),
+    writer.write(1),
+    writer.write(2e-16)
+  ];
+
+  assert_equals(writer.desiredSize, 0 - 1e-16 - 1 - 2e-16,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (after writing three chunks)');
+
+  return Promise.all(writePromises).then(() => {
+    assert_equals(writer.desiredSize, 0 - 1e-16 - 1 - 2e-16 + 1e-16 + 1 + 2e-16,
+      'desiredSize must be calculated using floating-point arithmetic (after the three chunks have finished writing)');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up positive, and not clamped)');
+
+promise_test(() => {
+  const writer = setupTestStream();
+
+  const writePromises = [
+    writer.write(2e-16),
+    writer.write(1)
+  ];
+
+  assert_equals(writer.desiredSize, 0 - 2e-16 - 1,
+    'desiredSize must be calculated using double-precision floating-point arithmetic (after writing two chunks)');
+
+  return Promise.all(writePromises).then(() => {
+    assert_equals(writer.desiredSize, 0 - 2e-16 - 1 + 2e-16 + 1,
+      'desiredSize must be calculated using floating-point arithmetic (after the two chunks have finished writing)');
+  });
+}, 'Floating point arithmetic must manifest near 0 (total ends up zero)');
+
+function setupTestStream() {
+  const strategy = {
+    size(x) {
+      return x;
+    },
+    highWaterMark: 0
+  };
+
+  const ws = new WritableStream({}, strategy);
+
+  return ws.getWriter();
+}