diff --git a/uasyncio_iostream/test_fast_scheduling.py b/uasyncio_iostream/test_fast_scheduling.py
new file mode 100644
index 0000000..104ed51
--- /dev/null
+++ b/uasyncio_iostream/test_fast_scheduling.py
@@ -0,0 +1,86 @@
+# iotest6.py Test fast_io PR
+# https://github.com/micropython/micropython-lib/pull/287
+
+# Test is designed to quantify the difference between fast and normal I/O without
+# recourse to electronic testgear.
+
+# The MyIO class supports .readline() which updates a call counter and clears the
+# .ready_rd flag. This is set by a timer (emulating the arrival of data from
+# some hardware device).
+# The .dummy method emulates a relatively slow user coro which yields with a zero
+# delay; the test runs 10 instances of this. Each instance updates a common call
+# counter.
+# The receiver coro awaits .readline continuously. With normal scheduling each is
+# scheduled after the ten .dummy instances have run. With fast scheduling and a
+# timer period <= 10ms readline and dummy alternate. If timer period is increased
+# readline is sheduled progressively less frequently.
+
+import io
+import pyb
+import utime
+import uasyncio as asyncio
+import micropython
+micropython.alloc_emergency_exception_buf(100)
+
+MP_STREAM_POLL_RD = const(1)
+MP_STREAM_POLL_WR = const(4)
+MP_STREAM_POLL = const(3)
+MP_STREAM_ERROR = const(-1)
+
+class MyIO(io.IOBase):
+    def __init__(self):
+        self.read_count = 0
+        self.dummy_count = 0
+        self.ready_rd = False
+        pyb.Timer(4, freq = 100, callback = self.do_input)
+
+    # Read callback: emulate asynchronous input from hardware.
+    def do_input(self, t):
+        self.ready_rd = True  # Data is ready to read
+
+    def ioctl(self, req, arg):
+        ret = MP_STREAM_ERROR
+        if req == MP_STREAM_POLL:
+            ret = 0
+            if arg & MP_STREAM_POLL_RD:
+                if self.ready_rd:
+                    ret |= MP_STREAM_POLL_RD
+        return ret
+
+    def readline(self):
+        self.read_count += 1
+        self.ready_rd = False
+        return b'a\n'
+
+    async def dummy(self):
+        while True:
+            await asyncio.sleep(0)
+            self.dummy_count += 1
+            utime.sleep_ms(10)  # Emulate time consuming user code
+
+    async def killer(self):
+        print('Test runs for 5s')
+        await asyncio.sleep(5)
+        print('I/O count {} Dummy count {}'.format(self.read_count, self.dummy_count))
+
+async def receiver(myior, fast):
+    sreader = asyncio.StreamReader(myior)
+    if fast:
+        sreader.priority()
+    while True:
+        await sreader.readline()
+
+def test(fast=False):
+    loop = asyncio.get_event_loop()
+    myior = MyIO()
+    loop.create_task(receiver(myior, fast))
+    for _ in range(10):
+        loop.create_task(myior.dummy())
+    loop.run_until_complete(myior.killer())
+
+print('Test case of I/O competing with zero delay tasks.')
+print('fast_io False: approx I/O count 25, dummy count 510.')
+print('fast_io True: approx I/O count 510, dummy count 510.')
+print('New uasyncio: I/O count 46, dummy 509.')
+print('Run test() to check I/O performance at normal priority.')
+print('Run test(True) to check I/O performance at high priority.')