title: Multiple async unit tests fail, but running them one by one will pass
body: <p>I have two unit tests, if I run them one by one, they pass.  If I run them at class level, one pass and the other one fails at <code>response = await ac.post(</code> with the error message: <code>RuntimeError: Event loop is closed</code></p>
  <pre><code>@pytest.mark.asyncio
  async def test_successful_register_saves_expiry_to_seven_days(self):
      async with AsyncClient(app=app, base_url=&quot;http://127.0.0.1&quot;) as ac:
          response = await ac.post(
              &quot;/register/&quot;,
              headers={},
              json={
                  &quot;device_id&quot;: &quot;u1&quot;,
                  &quot;device_type&quot;: DeviceType.IPHONE.value,
              },
          )
          query = device.select(whereclause=device.c.id == &quot;u1&quot;)
          d = await db.fetch_one(query)
          assert d.expires_at == datetime.utcnow().replace(
              second=0, microsecond=0
          ) + timedelta(days=7)
  
  @pytest.mark.asyncio
  async def test_successful_register_saves_device_type(self):
      async with AsyncClient(app=app, base_url=&quot;http://127.0.0.1&quot;) as ac:
          response = await ac.post(
              &quot;/register/&quot;,
              headers={},
              json={
                  &quot;device_id&quot;: &quot;u1&quot;,
                  &quot;device_type&quot;: DeviceType.ANDROID.value,
              },
          )
          query = device.select(whereclause=device.c.id == &quot;u1&quot;)
          d = await db.fetch_one(query)
          assert d.type == DeviceType.ANDROID.value
  </code></pre>
  <p>I have been trying for hours, what am I missing please?</p>