tests/micropython: Add new schedule_sleep.py test.

This variant of `schedule.py` explicitly calls a zero sleep.  The existing
variant is kept to ensure the scheduler is called between bytecodes.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>

tests/micropython/schedule.py

@@ -1,4 +1,6 @@
 # test micropython.schedule() function
+# this test should be manually kept in synch with
+# tests/micrpython/schedule_sleep.py.
 
 try:
     import micropython

tests/micropython/schedule_sleep.py

@@ -0,0 +1,72 @@
+# test micropython.schedule() function
+# this is the same as tests/micropython/schedule.py but the busy loops are
+# replaced with sleep/sleep_ms which allows the test to succeed when run under
+# the native emitter.
+
+try:
+    import micropython
+    import time
+
+    micropython.schedule
+except (ImportError, AttributeError):
+    print("SKIP")
+    raise SystemExit
+
+
+# Basic test of scheduling a function.
+
+
+def callback(arg):
+    global done
+    print(arg)
+    done = True
+
+
+done = False
+micropython.schedule(callback, 1)
+while not done:
+    time.sleep(0)
+
+# Test that callbacks can be scheduled from within a callback, but
+# that they don't execute until the outer callback is finished.
+
+
+def callback_inner(arg):
+    global done
+    print("inner")
+    done += 1
+
+
+def callback_outer(arg):
+    global done
+    micropython.schedule(callback_inner, 0)
+    # need a loop so that the VM can check for pending events
+    for i in range(2):
+        pass
+    print("outer")
+    done += 1
+
+
+done = 0
+micropython.schedule(callback_outer, 0)
+while done != 2:
+    time.sleep(0)
+
+# Test that scheduling too many callbacks leads to an exception.  To do this we
+# must schedule from within a callback to guarantee that the scheduler is locked.
+
+
+def callback(arg):
+    global done
+    try:
+        for i in range(100):
+            micropython.schedule(lambda x: x, None)
+    except RuntimeError:
+        print("RuntimeError")
+    done = True
+
+
+done = False
+micropython.schedule(callback, None)
+while not done:
+    time.sleep_ms(0)

tests/micropython/schedule_sleep.py.exp

@@ -0,0 +1,4 @@
+1
+outer
+inner
+RuntimeError

tests/run-tests.py

@@ -164,7 +164,7 @@ emitter_tests_to_skip = {
         "basics/exception_chain.py",
         # These require stack-allocated slice optimisation.
         "micropython/heapalloc_slice.py",
-        # These require running the scheduler.
+        # These require implicitly running the scheduler between bytecodes.
         "micropython/schedule.py",
         "extmod/asyncio_event_queue.py",
         "extmod/asyncio_iterator_event.py",