Add pytest-xdist support

Fixes #201.

Author: adamchainz

HISTORY.rst

@@ -2,6 +2,13 @@
 History
 -------
 
+* Add `pytest-xdist <https://pypi.org/project/pytest-xdist/>`__ support.
+  Previously it only worked reliably when setting ``--randomly-seed``
+  explicitly. When not provided, the default seed generated in workers could
+  differ and collection would fail. Now when it is not provided, all xdist
+  worker processes shared the same default seed generated in the master
+  process.
+
 3.2.1 (2020-01-13)
 ------------------
 

requirements/py35.txt

@@ -4,6 +4,10 @@
 #
 #    requirements/compile.py
 #
+apipkg==1.5 \
+    --hash=sha256:37228cda29411948b422fae072f57e31d3396d2ee1c9783775980ee9c9990af6 \
+    --hash=sha256:58587dd4dc3daefad0487f6d9ae32b4542b185e1c36db6993290e7c41ca2b47c \
+    # via execnet
 attrs==19.3.0 \
     --hash=sha256:08a96c641c3a74e44eb59afb61a24f2cb9f4d7188748e76ba4bb5edfa3cb7d1c \
     --hash=sha256:f7b7ce16570fe9965acd6d30101a28f62fb4a7f9e926b3bbc9b61f8b04247e72 \
@@ -79,6 +83,10 @@ entrypoints==0.3 \
     --hash=sha256:589f874b313739ad35be6e0cd7efde2a4e9b6fea91edcc34e58ecbb8dbe56d19 \
     --hash=sha256:c70dd71abe5a8c85e55e12c19bd91ccfeec11a6e99044204511f9ed547d48451 \
     # via flake8
+execnet==1.7.1 \
+    --hash=sha256:cacb9df31c9680ec5f95553976c4da484d407e85e41c83cb812aa014f0eddc50 \
+    --hash=sha256:d4efd397930c46415f62f8a31388d6be4f27a91d7550eb79bc64a756e0056547 \
+    # via pytest-xdist
 factory-boy==2.12.0 \
     --hash=sha256:728df59b372c9588b83153facf26d3d28947fc750e8e3c95cefa9bed0e6394ee \
     --hash=sha256:faf48d608a1735f0d0a3c9cbf536d64f9132b547dae7ba452c4d99a79e84a370 \
@@ -194,10 +202,18 @@ pyparsing==2.4.7 \
     --hash=sha256:c203ec8783bf771a155b207279b9bccb8dea02d8f0c9e5f8ead507bc3246ecc1 \
     --hash=sha256:ef9d7589ef3c200abe66653d3f1ab1033c3c419ae9b9bdb1240a85b024efc88b \
     # via packaging
+pytest-forked==1.1.3 \
+    --hash=sha256:1805699ed9c9e60cb7a8179b8d4fa2b8898098e82d229b0825d8095f0f261100 \
+    --hash=sha256:1ae25dba8ee2e56fb47311c9638f9e58552691da87e82d25b0ce0e4bf52b7d87 \
+    # via pytest-xdist
+pytest-xdist==1.31.0 \
+    --hash=sha256:0f46020d3d9619e6d17a65b5b989c1ebbb58fc7b1da8fb126d70f4bac4dfeed1 \
+    --hash=sha256:7dc0d027d258cd0defc618fb97055fbd1002735ca7a6d17037018cf870e24011 \
+    # via -r requirements.in
 pytest==5.4.1 \
     --hash=sha256:0e5b30f5cb04e887b91b1ee519fa3d89049595f428c1db76e73bd7f17b09b172 \
     --hash=sha256:84dde37075b8805f3d1f392cc47e38a0e59518fb46a431cfdaf7cf1ce805f970 \
-    # via -r requirements.in
+    # via -r requirements.in, pytest-forked, pytest-xdist
 python-dateutil==2.8.1 \
     --hash=sha256:73ebfe9dbf22e832286dafa60473e4cd239f8592f699aa5adaf10050e6e1823c \
     --hash=sha256:75bb3f31ea686f1197762692a9ee6a7550b59fc6ca3a1f4b5d7e32fb98e2da2a \
@@ -221,7 +237,7 @@ secretstorage==3.1.2 \
 six==1.14.0 \
     --hash=sha256:236bdbdce46e6e6a3d61a337c0f8b763ca1e8717c03b369e87a7ec7ce1319c0a \
     --hash=sha256:8f3cd2e254d8f793e7f3d6d9df77b92252b52637291d0f0da013c76ea2724b6c \
-    # via bleach, cryptography, packaging, pathlib2, python-dateutil, readme-renderer
+    # via bleach, cryptography, packaging, pathlib2, pytest-xdist, python-dateutil, readme-renderer
 text-unidecode==1.3 \
     --hash=sha256:1311f10e8b895935241623731c2ba64f4c455287888b18189350b67134a822e8 \
     --hash=sha256:bad6603bb14d279193107714b288be206cac565dfa49aa5b105294dd5c4aab93 \

requirements/py36.txt

@@ -4,6 +4,10 @@
 #
 #    requirements/compile.py
 #
+apipkg==1.5 \
+    --hash=sha256:37228cda29411948b422fae072f57e31d3396d2ee1c9783775980ee9c9990af6 \
+    --hash=sha256:58587dd4dc3daefad0487f6d9ae32b4542b185e1c36db6993290e7c41ca2b47c \
+    # via execnet
 attrs==19.3.0 \
     --hash=sha256:08a96c641c3a74e44eb59afb61a24f2cb9f4d7188748e76ba4bb5edfa3cb7d1c \
     --hash=sha256:f7b7ce16570fe9965acd6d30101a28f62fb4a7f9e926b3bbc9b61f8b04247e72 \
@@ -79,6 +83,10 @@ entrypoints==0.3 \
     --hash=sha256:589f874b313739ad35be6e0cd7efde2a4e9b6fea91edcc34e58ecbb8dbe56d19 \
     --hash=sha256:c70dd71abe5a8c85e55e12c19bd91ccfeec11a6e99044204511f9ed547d48451 \
     # via flake8
+execnet==1.7.1 \
+    --hash=sha256:cacb9df31c9680ec5f95553976c4da484d407e85e41c83cb812aa014f0eddc50 \
+    --hash=sha256:d4efd397930c46415f62f8a31388d6be4f27a91d7550eb79bc64a756e0056547 \
+    # via pytest-xdist
 factory-boy==2.12.0 \
     --hash=sha256:728df59b372c9588b83153facf26d3d28947fc750e8e3c95cefa9bed0e6394ee \
     --hash=sha256:faf48d608a1735f0d0a3c9cbf536d64f9132b547dae7ba452c4d99a79e84a370 \
@@ -194,10 +202,18 @@ pyparsing==2.4.7 \
     --hash=sha256:c203ec8783bf771a155b207279b9bccb8dea02d8f0c9e5f8ead507bc3246ecc1 \
     --hash=sha256:ef9d7589ef3c200abe66653d3f1ab1033c3c419ae9b9bdb1240a85b024efc88b \
     # via packaging
+pytest-forked==1.1.3 \
+    --hash=sha256:1805699ed9c9e60cb7a8179b8d4fa2b8898098e82d229b0825d8095f0f261100 \
+    --hash=sha256:1ae25dba8ee2e56fb47311c9638f9e58552691da87e82d25b0ce0e4bf52b7d87 \
+    # via pytest-xdist
+pytest-xdist==1.31.0 \
+    --hash=sha256:0f46020d3d9619e6d17a65b5b989c1ebbb58fc7b1da8fb126d70f4bac4dfeed1 \
+    --hash=sha256:7dc0d027d258cd0defc618fb97055fbd1002735ca7a6d17037018cf870e24011 \
+    # via -r requirements.in
 pytest==5.4.1 \
     --hash=sha256:0e5b30f5cb04e887b91b1ee519fa3d89049595f428c1db76e73bd7f17b09b172 \
     --hash=sha256:84dde37075b8805f3d1f392cc47e38a0e59518fb46a431cfdaf7cf1ce805f970 \
-    # via -r requirements.in
+    # via -r requirements.in, pytest-forked, pytest-xdist
 python-dateutil==2.8.1 \
     --hash=sha256:73ebfe9dbf22e832286dafa60473e4cd239f8592f699aa5adaf10050e6e1823c \
     --hash=sha256:75bb3f31ea686f1197762692a9ee6a7550b59fc6ca3a1f4b5d7e32fb98e2da2a \
@@ -221,7 +237,7 @@ secretstorage==3.1.2 \
 six==1.14.0 \
     --hash=sha256:236bdbdce46e6e6a3d61a337c0f8b763ca1e8717c03b369e87a7ec7ce1319c0a \
     --hash=sha256:8f3cd2e254d8f793e7f3d6d9df77b92252b52637291d0f0da013c76ea2724b6c \
-    # via bleach, cryptography, packaging, python-dateutil, readme-renderer
+    # via bleach, cryptography, packaging, pytest-xdist, python-dateutil, readme-renderer
 text-unidecode==1.3 \
     --hash=sha256:1311f10e8b895935241623731c2ba64f4c455287888b18189350b67134a822e8 \
     --hash=sha256:bad6603bb14d279193107714b288be206cac565dfa49aa5b105294dd5c4aab93 \

requirements/py37.txt

@@ -4,6 +4,10 @@
 #
 #    requirements/compile.py
 #
+apipkg==1.5 \
+    --hash=sha256:37228cda29411948b422fae072f57e31d3396d2ee1c9783775980ee9c9990af6 \
+    --hash=sha256:58587dd4dc3daefad0487f6d9ae32b4542b185e1c36db6993290e7c41ca2b47c \
+    # via execnet
 attrs==19.3.0 \
     --hash=sha256:08a96c641c3a74e44eb59afb61a24f2cb9f4d7188748e76ba4bb5edfa3cb7d1c \
     --hash=sha256:f7b7ce16570fe9965acd6d30101a28f62fb4a7f9e926b3bbc9b61f8b04247e72 \
@@ -79,6 +83,10 @@ entrypoints==0.3 \
     --hash=sha256:589f874b313739ad35be6e0cd7efde2a4e9b6fea91edcc34e58ecbb8dbe56d19 \
     --hash=sha256:c70dd71abe5a8c85e55e12c19bd91ccfeec11a6e99044204511f9ed547d48451 \
     # via flake8
+execnet==1.7.1 \
+    --hash=sha256:cacb9df31c9680ec5f95553976c4da484d407e85e41c83cb812aa014f0eddc50 \
+    --hash=sha256:d4efd397930c46415f62f8a31388d6be4f27a91d7550eb79bc64a756e0056547 \
+    # via pytest-xdist
 factory-boy==2.12.0 \
     --hash=sha256:728df59b372c9588b83153facf26d3d28947fc750e8e3c95cefa9bed0e6394ee \
     --hash=sha256:faf48d608a1735f0d0a3c9cbf536d64f9132b547dae7ba452c4d99a79e84a370 \
@@ -194,10 +202,18 @@ pyparsing==2.4.7 \
     --hash=sha256:c203ec8783bf771a155b207279b9bccb8dea02d8f0c9e5f8ead507bc3246ecc1 \
     --hash=sha256:ef9d7589ef3c200abe66653d3f1ab1033c3c419ae9b9bdb1240a85b024efc88b \
     # via packaging
+pytest-forked==1.1.3 \
+    --hash=sha256:1805699ed9c9e60cb7a8179b8d4fa2b8898098e82d229b0825d8095f0f261100 \
+    --hash=sha256:1ae25dba8ee2e56fb47311c9638f9e58552691da87e82d25b0ce0e4bf52b7d87 \
+    # via pytest-xdist
+pytest-xdist==1.31.0 \
+    --hash=sha256:0f46020d3d9619e6d17a65b5b989c1ebbb58fc7b1da8fb126d70f4bac4dfeed1 \
+    --hash=sha256:7dc0d027d258cd0defc618fb97055fbd1002735ca7a6d17037018cf870e24011 \
+    # via -r requirements.in
 pytest==5.4.1 \
     --hash=sha256:0e5b30f5cb04e887b91b1ee519fa3d89049595f428c1db76e73bd7f17b09b172 \
     --hash=sha256:84dde37075b8805f3d1f392cc47e38a0e59518fb46a431cfdaf7cf1ce805f970 \
-    # via -r requirements.in
+    # via -r requirements.in, pytest-forked, pytest-xdist
 python-dateutil==2.8.1 \
     --hash=sha256:73ebfe9dbf22e832286dafa60473e4cd239f8592f699aa5adaf10050e6e1823c \
     --hash=sha256:75bb3f31ea686f1197762692a9ee6a7550b59fc6ca3a1f4b5d7e32fb98e2da2a \
@@ -221,7 +237,7 @@ secretstorage==3.1.2 \
 six==1.14.0 \
     --hash=sha256:236bdbdce46e6e6a3d61a337c0f8b763ca1e8717c03b369e87a7ec7ce1319c0a \
     --hash=sha256:8f3cd2e254d8f793e7f3d6d9df77b92252b52637291d0f0da013c76ea2724b6c \
-    # via bleach, cryptography, packaging, python-dateutil, readme-renderer
+    # via bleach, cryptography, packaging, pytest-xdist, python-dateutil, readme-renderer
 text-unidecode==1.3 \
     --hash=sha256:1311f10e8b895935241623731c2ba64f4c455287888b18189350b67134a822e8 \
     --hash=sha256:bad6603bb14d279193107714b288be206cac565dfa49aa5b105294dd5c4aab93 \

requirements/py38.txt

@@ -4,6 +4,10 @@
 #
 #    requirements/compile.py
 #
+apipkg==1.5 \
+    --hash=sha256:37228cda29411948b422fae072f57e31d3396d2ee1c9783775980ee9c9990af6 \
+    --hash=sha256:58587dd4dc3daefad0487f6d9ae32b4542b185e1c36db6993290e7c41ca2b47c \
+    # via execnet
 appdirs==1.4.3 \
     --hash=sha256:9e5896d1372858f8dd3344faf4e5014d21849c756c8d5701f78f8a103b372d92 \
     --hash=sha256:d8b24664561d0d34ddfaec54636d502d7cea6e29c3eaf68f3df6180863e2166e \
@@ -95,6 +99,10 @@ entrypoints==0.3 \
     --hash=sha256:589f874b313739ad35be6e0cd7efde2a4e9b6fea91edcc34e58ecbb8dbe56d19 \
     --hash=sha256:c70dd71abe5a8c85e55e12c19bd91ccfeec11a6e99044204511f9ed547d48451 \
     # via flake8
+execnet==1.7.1 \
+    --hash=sha256:cacb9df31c9680ec5f95553976c4da484d407e85e41c83cb812aa014f0eddc50 \
+    --hash=sha256:d4efd397930c46415f62f8a31388d6be4f27a91d7550eb79bc64a756e0056547 \
+    # via pytest-xdist
 factory-boy==2.12.0 \
     --hash=sha256:728df59b372c9588b83153facf26d3d28947fc750e8e3c95cefa9bed0e6394ee \
     --hash=sha256:faf48d608a1735f0d0a3c9cbf536d64f9132b547dae7ba452c4d99a79e84a370 \
@@ -214,10 +222,18 @@ pyparsing==2.4.7 \
     --hash=sha256:c203ec8783bf771a155b207279b9bccb8dea02d8f0c9e5f8ead507bc3246ecc1 \
     --hash=sha256:ef9d7589ef3c200abe66653d3f1ab1033c3c419ae9b9bdb1240a85b024efc88b \
     # via packaging
+pytest-forked==1.1.3 \
+    --hash=sha256:1805699ed9c9e60cb7a8179b8d4fa2b8898098e82d229b0825d8095f0f261100 \
+    --hash=sha256:1ae25dba8ee2e56fb47311c9638f9e58552691da87e82d25b0ce0e4bf52b7d87 \
+    # via pytest-xdist
+pytest-xdist==1.31.0 \
+    --hash=sha256:0f46020d3d9619e6d17a65b5b989c1ebbb58fc7b1da8fb126d70f4bac4dfeed1 \
+    --hash=sha256:7dc0d027d258cd0defc618fb97055fbd1002735ca7a6d17037018cf870e24011 \
+    # via -r requirements.in
 pytest==5.4.1 \
     --hash=sha256:0e5b30f5cb04e887b91b1ee519fa3d89049595f428c1db76e73bd7f17b09b172 \
     --hash=sha256:84dde37075b8805f3d1f392cc47e38a0e59518fb46a431cfdaf7cf1ce805f970 \
-    # via -r requirements.in
+    # via -r requirements.in, pytest-forked, pytest-xdist
 python-dateutil==2.8.1 \
     --hash=sha256:73ebfe9dbf22e832286dafa60473e4cd239f8592f699aa5adaf10050e6e1823c \
     --hash=sha256:75bb3f31ea686f1197762692a9ee6a7550b59fc6ca3a1f4b5d7e32fb98e2da2a \
@@ -264,7 +280,7 @@ secretstorage==3.1.2 \
 six==1.14.0 \
     --hash=sha256:236bdbdce46e6e6a3d61a337c0f8b763ca1e8717c03b369e87a7ec7ce1319c0a \
     --hash=sha256:8f3cd2e254d8f793e7f3d6d9df77b92252b52637291d0f0da013c76ea2724b6c \
-    # via bleach, cryptography, packaging, python-dateutil, readme-renderer
+    # via bleach, cryptography, packaging, pytest-xdist, python-dateutil, readme-renderer
 text-unidecode==1.3 \
     --hash=sha256:1311f10e8b895935241623731c2ba64f4c455287888b18189350b67134a822e8 \
     --hash=sha256:bad6603bb14d279193107714b288be206cac565dfa49aa5b105294dd5c4aab93 \

requirements/requirements.in

@@ -13,5 +13,6 @@ multilint
 numpy
 pygments
 pytest
+pytest-xdist
 secretstorage # required for twine on linux
 twine

src/pytest_randomly.py

@@ -46,7 +46,7 @@
 
 
 def seed_type(string):
-    if string == "last":
+    if string in ("default", "last"):
         return string
     try:
         return int(string)
@@ -62,7 +62,7 @@ def pytest_addoption(parser):
         "--randomly-seed",
         action="store",
         dest="randomly_seed",
-        default=str(default_seed),
+        default="default",
         type=seed_type,
         help="""Set the seed that pytest-randomly uses (int), or pass the
                 special value 'last' to reuse the seed from the previous run.
@@ -87,6 +87,29 @@ def pytest_addoption(parser):
     )
 
 
+def pytest_configure(config):
+    seed_value = config.getoption("randomly_seed")
+    if seed_value == "last":
+        seed = config.cache.get("randomly_seed", default_seed)
+    elif seed_value == "default":
+        if hasattr(config, "workerinput"):
+            # pytest-xdist: use seed generated on master.
+            seed = config.workerinput["randomly_seed"]
+        else:
+            seed = default_seed
+    else:
+        seed = seed_value
+    config.cache.set("randomly_seed", seed)
+    config.option.randomly_seed = seed
+
+
+def pytest_configure_node(node):
+    """
+    pytest-xdist hook. Send the selected seed through to the nodes.
+    """
+    node.workerinput["randomly_seed"] = node.config.getoption("randomly_seed")
+
+
 random_states = {}
 np_random_states = {}
 
@@ -125,13 +148,7 @@ def _reseed(config, offset=0):
 
 
 def pytest_report_header(config):
-    seed_value = config.getoption("randomly_seed")
-    if seed_value == "last":
-        seed = config.cache.get("randomly_seed", default_seed)
-    else:
-        seed = seed_value
-    config.cache.set("randomly_seed", seed)
-    config.option.randomly_seed = seed
+    seed = config.getoption("randomly_seed")
     _reseed(config)
     return "Using --randomly-seed={}".format(seed)
 

tests/test_pytest_randomly.py

@@ -668,3 +668,25 @@ def fake_entry_points():
 
     # Need to run in-process so that monkeypatching works
     testdir.runpytest("--randomly-seed=1")
+
+
+@pytest.mark.parametrize("n", list(range(5)))
+def test_xdist(n, ourtestdir):
+    """
+    This test does not expose the original bug (non-shared default seeds) with
+    a very high probability, hence multiple runs.
+    """
+    ourtestdir.makepyfile(
+        test_one="def test_a(): pass",
+        test_two="def test_a(): pass",
+        test_three="def test_a(): pass",
+        test_four="def test_a(): pass",
+        test_five="def test_a(): pass",
+        test_six="def test_a(): pass",
+    )
+
+    out = ourtestdir.runpytest("-n 6", "-v", "--dist=loadfile")
+    out.assert_outcomes(passed=6)
+
+    # Can't make any assertion on the order, since output comes back from
+    # workers non-deterministically