Convert runtest.py to use pytest. (#2966)

* Convert runtest.py to use pytest.

* Linting.

* Fix

* Fix

* Fix

* Fix

.travis.yml

@@ -135,10 +135,7 @@ matrix:
         - python -m pytest -v python/ray/test/test_queue.py
         - python -m pytest -v test/xray_test.py
 
-        # The --assert=plain here is because pytest's assertion
-        # rewriting mechanism seems to mess up on this file,
-        # see https://github.com/ray-project/ray/issues/2514
-        - python -m pytest -v --assert=plain test/runtest.py
+        - python -m pytest -v test/runtest.py
         - python -m pytest -v test/array_test.py
         - python -m pytest -v test/actor_test.py
         - python -m pytest -v test/autoscaler_test.py
@@ -210,10 +207,7 @@ script:
   - python -m pytest -v python/ray/test/test_queue.py
   - python -m pytest -v test/xray_test.py
 
-  # The --assert=plain here is because pytest's assertion
-  # rewriting mechanism seems to mess up on this file,
-  # see https://github.com/ray-project/ray/issues/2514
-  - python -m pytest --assert=plain -v test/runtest.py
+  - python -m pytest -v test/runtest.py
   - python -m pytest -v test/array_test.py
   - python -m pytest -v test/actor_test.py
   - python -m pytest -v test/autoscaler_test.py

test/stress_tests.py

@@ -11,11 +11,20 @@ import ray
 import ray.ray_constants as ray_constants
 
 
-@pytest.fixture
-def ray_start_regular():
+@pytest.fixture(params=[1, 20])
+def ray_start_sharded(request):
+    num_redis_shards = request.param
+
+    if os.environ.get("RAY_USE_NEW_GCS") == "on":
+        num_redis_shards = 1
+        # For now, RAY_USE_NEW_GCS supports 1 shard, and credis supports
+        # 1-node chain for that shard only.
+
     # Start the Ray processes.
-    ray.init(num_cpus=10)
+    ray.init(num_cpus=10, num_redis_shards=num_redis_shards)
+
     yield None
+
     # The code after the yield will run as teardown code.
     ray.shutdown()
 
@@ -78,7 +87,7 @@ def test_dependencies(ray_start_combination):
     assert ray.services.all_processes_alive()
 
 
-def test_submitting_many_tasks(ray_start_regular):
+def test_submitting_many_tasks(ray_start_sharded):
     @ray.remote
     def f(x):
         return 1
@@ -93,7 +102,7 @@ def test_submitting_many_tasks(ray_start_regular):
     assert ray.services.all_processes_alive()
 
 
-def test_getting_and_putting(ray_start_regular):
+def test_getting_and_putting(ray_start_sharded):
     for n in range(8):
         x = np.zeros(10**n)
 
@@ -107,7 +116,7 @@ def test_getting_and_putting(ray_start_regular):
     assert ray.services.all_processes_alive()
 
 
-def test_getting_many_objects(ray_start_regular):
+def test_getting_many_objects(ray_start_sharded):
     @ray.remote
     def f():
         return 1