Add an option to skip thread-unsafe tests

Author: ngoldbaum

README.md

@@ -61,9 +61,11 @@ those fixtures are shared between threads.
 
 ## Features
 
-- Two global CLI flags:
+- Three global CLI flags:
     - `--parallel-threads` to run a test suite in parallel
     - `--iterations` to run multiple times in each thread
+    - `--skip-thread-unsafe` to skip running tests marked as or
+      detected to be thread-unsafe.
 
 - Three corresponding markers:
     - `pytest.mark.parallel_threads(n)` to mark a single test to run
@@ -239,6 +241,12 @@ def test_skip_if_parallel(num_parallel_threads):
     ...
 ```
 
+You can skip tests marked as or detected to be thread-unsafe by passing
+`--skip-thread-unsafe` in your pytest invocation. This is useful when running
+pytest-run-parallel under [Thread Sanitizer](). Setting
+`--skip-thread-unsafe=True` will avoid unnecessarily running tests where thread
+sanitizer cannot detect races because the test is not parallelized.
+
 Finally, the `thread_comp` fixture allows for parallel test debugging,
 by providing an instance of `ThreadComparator`, whose `__call__` method
 allows to check if all the values produced by all threads during an

src/pytest_run_parallel/plugin.py

@@ -32,6 +32,14 @@ def pytest_addoption(parser):
         type=int,
         help="Set the number of threads used to execute each test concurrently.",
     )
+    parser.addoption(
+        "--skip-thread-unsafe",
+        action="store",
+        dest="skip_thread_unsafe",
+        help="Whether to skip running thread-unsafe tests",
+        type=bool,
+        default=False,
+    )
     parser.addini(
         "thread_unsafe_fixtures",
         "list of thread-unsafe fixture names that cause a test to "
@@ -145,6 +153,8 @@ def pytest_itemcollected(item):
     fixtures = getattr(item, "fixturenames", ())
 
     n_iterations = item.config.option.iterations
+    skip_thread_unsafe = item.config.option.skip_thread_unsafe
+
     m = item.get_closest_marker("iterations")
     if m is not None:
         n_iterations = int(m.args[0])
@@ -153,13 +163,14 @@ def pytest_itemcollected(item):
     if n_workers > 1 and m is not None:
         n_workers = 1
         reason = m.kwargs.get("reason", None)
-        if reason is not None:
-            item.user_properties.append(("thread_unsafe_reason", reason))
+        if reason is None:
+            reason = "uses thread_unsafe marker"
+        item.user_properties.append(("thread_unsafe_reason", reason))
+        if skip_thread_unsafe:
+            item.add_marker(pytest.mark.skip(
+                reason=f"Thread unsafe: {reason}"))
         else:
-            item.user_properties.append(
-                ("thread_unsafe_reason", "uses thread_unsafe marker")
-            )
-        item.add_marker(pytest.mark.parallel_threads(1))
+            item.add_marker(pytest.mark.parallel_threads(1))
 
     if not hasattr(item, "obj"):
         if hasattr(item, "_parallel_custom_item"):
@@ -183,14 +194,20 @@ def pytest_itemcollected(item):
     ]
     skipped_functions = frozenset((".".join(x[:-1]), x[-1]) for x in skipped_functions)
 
+    skip_thread_unsafe = item.config.option.skip_thread_unsafe
+
     if n_workers > 1:
         thread_unsafe, thread_unsafe_reason = identify_thread_unsafe_nodes(
             item.obj, skipped_functions
         )
         if thread_unsafe:
             n_workers = 1
             item.user_properties.append(("thread_unsafe_reason", thread_unsafe_reason))
-            item.add_marker(pytest.mark.parallel_threads(1))
+            if skip_thread_unsafe:
+                item.add_marker(pytest.mark.skip(
+                    reason=f"Thread unsafe: {thread_unsafe_reason}"))
+            else:
+                item.add_marker(pytest.mark.parallel_threads(1))
 
     unsafe_fixtures = _thread_unsafe_fixtures | set(
         item.config.getini("thread_unsafe_fixtures")

tests/test_run_parallel.py

@@ -589,6 +589,16 @@ def test_should_run_single_2(num_parallel_threads):
         ]
     )
 
+    # check that skipping works too
+    result = pytester.runpytest(
+        "--parallel-threads=10", "--skip-thread-unsafe=True", "-v")
+
+    result.stdout.fnmatch_lines([
+        "*::test_should_run_single SKIPPED*",
+        "*::test_should_run_single_2 SKIPPED*"
+        ]
+    )
+
 
 def test_pytest_warns_detection(pytester):
     # create a temporary pytest test module
@@ -636,6 +646,18 @@ def test_single_thread_warns_4(num_parallel_threads):
         ]
     )
 
+    # check that skipping works too
+    result = pytester.runpytest(
+        "--parallel-threads=10", "--skip-thread-unsafe=True", "-v")
+
+    result.stdout.fnmatch_lines(
+        [
+            "*::test_single_thread_warns_1 SKIPPED*",
+            "*::test_single_thread_warns_2 SKIPPED*",
+            "*::test_single_thread_warns_3 SKIPPED*",
+            "*::test_single_thread_warns_4 SKIPPED*",
+        ]
+    )
 
 @pytest.mark.skipif(psutil is None, reason="psutil needs to be installed")
 def test_auto_detect_cpus_psutil_affinity(