tests: Add 6 tests for async await/for/with.

tests/basics/async_await.py

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+# test basic await expression
+# adapted from PEP0492
+
+async def abinary(n):
+    print(n)
+    if n <= 0:
+        return 1
+    l = await abinary(n - 1)
+    r = await abinary(n - 1)
+    return l + 1 + r
+
+o = abinary(4)
+try:
+    while True:
+        o.send(None)
+except StopIteration:
+    print('finished')

tests/basics/async_await2.py

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+# test await expression
+
+import sys
+if sys.implementation.name == 'micropython':
+    # uPy allows normal generators to be awaitables
+    coroutine = lambda f: f
+else:
+    import types
+    coroutine = types.coroutine
+
+@coroutine
+def wait(value):
+    print('wait value:', value)
+    msg = yield 'message from wait(%u)' % value
+    print('wait got back:', msg)
+    return 10
+
+async def f():
+    x = await wait(1)**2
+    print('x =', x)
+
+coro = f()
+print('return from send:', coro.send(None))
+try:
+    coro.send('message from main')
+except StopIteration:
+    print('got StopIteration')

tests/basics/async_for.py

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+# test basic async for execution
+# example taken from PEP0492
+
+class AsyncIteratorWrapper:
+    def __init__(self, obj):
+        print('init')
+        self._it = iter(obj)
+
+    async def __aiter__(self):
+        print('aiter')
+        return self
+
+    async def __anext__(self):
+        print('anext')
+        try:
+            value = next(self._it)
+        except StopIteration:
+            raise StopAsyncIteration
+        return value
+
+async def coro():
+    async for letter in AsyncIteratorWrapper('abc'):
+        print(letter)
+
+o = coro()
+try:
+    o.send(None)
+except StopIteration:
+    print('finished')

tests/basics/async_for2.py

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+# test waiting within "async for" aiter/anext functions
+
+import sys
+if sys.implementation.name == 'micropython':
+    # uPy allows normal generators to be awaitables
+    coroutine = lambda f: f
+else:
+    import types
+    coroutine = types.coroutine
+
+@coroutine
+def f(x):
+    print('f start:', x)
+    yield x + 1
+    yield x + 2
+    return x + 3
+
+class ARange:
+    def __init__(self, high):
+        print('init')
+        self.cur = 0
+        self.high = high
+
+    async def __aiter__(self):
+        print('aiter')
+        print('f returned:', await f(10))
+        return self
+
+    async def __anext__(self):
+        print('anext')
+        print('f returned:', await f(20))
+        if self.cur < self.high:
+            val = self.cur
+            self.cur += 1
+            return val
+        else:
+            raise StopAsyncIteration
+
+async def coro():
+    async for x in ARange(4):
+        print('x', x)
+
+o = coro()
+try:
+    while True:
+        print('coro yielded:', o.send(None))
+except StopIteration:
+    print('finished')

tests/basics/async_with.py

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+# test simple async with execution
+
+class AContext:
+    async def __aenter__(self):
+        print('enter')
+    async def __aexit__(self, exc_type, exc, tb):
+        print('exit')
+
+async def f():
+    async with AContext():
+        print('body')
+
+o = f()
+try:
+    o.send(None)
+except StopIteration:
+    print('finished')

tests/basics/async_with2.py

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+# test waiting within async with enter/exit functions
+
+import sys
+if sys.implementation.name == 'micropython':
+    # uPy allows normal generators to be awaitables
+    coroutine = lambda f: f
+else:
+    import types
+    coroutine = types.coroutine
+
+@coroutine
+def f(x):
+    print('f start:', x)
+    yield x + 1
+    yield x + 2
+    return x + 3
+
+class AContext:
+    async def __aenter__(self):
+        print('enter')
+        print('f returned:', await f(10))
+    async def __aexit__(self, exc_type, exc, tb):
+        print('exit')
+        print('f returned:', await f(20))
+
+async def coro():
+    async with AContext():
+        print('body start')
+        print('body f returned:', await f(30))
+        print('body end')
+
+o = coro()
+try:
+    while True:
+        print('coro yielded:', o.send(None))
+except StopIteration:
+    print('finished')