Convert nh2.mock.expect_connect to a context manager.

Assert that the expected connection has been established before the context manager ends, similar to:

  mock_server = await nh2.mock.expect_connect(…)
  conn = await nh2.connection.Connection(…)
  assert conn.mock_server is mock_server

Note that sometimes tests only imply a connection, they don't explicitly set one themselves, as in:

  async def opaque_workflow():
      conn = await nh2.connection.Connection('example.com', 443)

  async with nh2.anyio_util.create_task_group() as tg:
      async with nh2.mock.expect_connect('example.com', 443) as mock_server:
          future = tg.start_soon(opaque_workflow)

so expect_connect needs to allow the async system to actually schedule and run backgrounded tasks (which for now is done with just an `anyio.sleep(.01)`).

Explicitly reset nh2.mock.expect_connect's cache between runs.

See #1.

nh2/_pytest_plugin.py

@@ -8,3 +8,4 @@
 @pytest.fixture(autouse=True)
 def _connection_mock(monkeypatch):
     monkeypatch.setattr('nh2.connection.Connection', nh2.mock.MockConnection)
+    monkeypatch.setattr('nh2.mock._servers', {})  # Don't let a failing test poison other tests.

nh2/mock.py

@@ -1,5 +1,6 @@
 """Utilities to control nh2 during tests."""
 
+import contextlib
 import textwrap
 
 import anyio
@@ -13,6 +14,7 @@
 _servers = {}
 
 
+@contextlib.asynccontextmanager
 async def expect_connect(host, port, *, live=False):
     """Prepare for an upcoming attempt to connect to host:port."""
 
@@ -22,7 +24,10 @@ async def expect_connect(host, port, *, live=False):
     else:
         server = await MockServer(host, port)
     _servers[host, port] = server
-    return server
+    yield server
+    if (host, port) in _servers:
+        await anyio.sleep(.01)
+        assert (host, port) not in _servers
 
 
 class MockConnection(nh2.connection.Connection):

nh2/test_connection.py

@@ -13,8 +13,8 @@
 async def test_simple():
     """Basic functionality."""
 
-    await nh2.mock.expect_connect('httpbin.org', 443, live=True)
-    conn = await nh2.connection.Connection('httpbin.org', 443)
+    async with nh2.mock.expect_connect('httpbin.org', 443, live=True):
+        conn = await nh2.connection.Connection('httpbin.org', 443)
     try:
         assert not conn.streams
         live_request = await conn.request('GET', '/get?a=b')
@@ -41,8 +41,8 @@ async def test_simple():
 async def test_concurrent_send():
     """Verify the Connection can handle multiple concurrent sends."""
 
-    await nh2.mock.expect_connect('httpbin.org', 443, live=True)
-    conn = await nh2.connection.Connection('httpbin.org', 443)
+    async with nh2.mock.expect_connect('httpbin.org', 443, live=True):
+        conn = await nh2.connection.Connection('httpbin.org', 443)
     try:
         async with anyio.create_task_group() as tg:
             tg.start_soon(conn.request, 'GET', '/get?a=1')
@@ -54,8 +54,8 @@ async def test_concurrent_send():
 async def test_concurrent_wait():
     """Verify the interaction between two concurrent LiveRequest.wait()s."""
 
-    await nh2.mock.expect_connect('httpbin.org', 443, live=True)
-    conn = await nh2.connection.Connection('httpbin.org', 443)
+    async with nh2.mock.expect_connect('httpbin.org', 443, live=True):
+        conn = await nh2.connection.Connection('httpbin.org', 443)
     try:
         res1 = res2 = None
 

nh2/test_mock.py

@@ -12,8 +12,8 @@
 async def test_simple():
     """Manually run a complete connection and request."""
 
-    mock_server = await nh2.mock.expect_connect('example.com', 443)
-    conn = await nh2.connection.Connection('example.com', 443)
+    async with nh2.mock.expect_connect('example.com', 443) as mock_server:
+        conn = await nh2.connection.Connection('example.com', 443)
     # On connect, client and server each send settings, but client does not block to receive them.
     assert mock_server.get_client_events() == ''
     assert await mock_server.read() == """
@@ -105,8 +105,8 @@ async def opaque_workflow():
         return 'finished'
 
     async with nh2.anyio_util.create_task_group() as tg:
-        mock_server = await nh2.mock.expect_connect('example.com', 443)
-        future = tg.start_soon(opaque_workflow)
+        async with nh2.mock.expect_connect('example.com', 443) as mock_server:
+            future = tg.start_soon(opaque_workflow)
 
         assert await mock_server.read() == """
           - [RemoteSettingsChanged header_table_size=4096 enable_push=1 initial_window_size=65535 max_frame_size=16384 enable_connect_protocol=0 max_concurrent_streams=100 max_header_list_size=65536]