Merge pull request #176 from ngoldbaum/force-parallel-threads

Add a force_parallel_threads mark

Author: ngoldbaum

README.md

@@ -93,12 +93,17 @@ those fixtures are shared between threads.
       as errors.
 
 
-- Four corresponding markers:
+- Five corresponding markers:
     - `pytest.mark.parallel_threads_limit(n)` to mark a single test to
         run in a maximum of `n` threads, even if the `--parallel-threads`
         command-line argument is set to a higher value. This is useful if a
         test uses resources that should be limited.
-    - `pytest.mark.parallel_threads(n)` to mark a test to always run in `n`
+    - `pytest.mark.force_parallel_threads(n)` to force a test to always run
+        in `n` threads, overriding both the `--parallel-threads` command-line
+        argument and any `parallel_threads_limit` marker. Use this when a
+        test must always be multi-threaded with a specific thread count.
+    - `pytest.mark.parallel_threads(n)` (deprecated when `n > 1` — use
+        `force_parallel_threads` instead) to mark a test to always run in `n`
         threads. Note that this implies that the test will be multi-threaded
         just because pytest-run-parallel is installed, even if
         `--parallel-threads` is not passed at the command-line.
@@ -130,8 +135,9 @@ temporary directory in that fixture.
 When using the fixtures `thread_index` and `iteration_index`, they should be
 requested directly by tests, and will return 0 when requested by other fixtures.
 
-**Note**: It's possible to specify `--parallel-threads=auto` or
-`pytest.mark.parallel_threads("auto")` which will let
+**Note**: It's possible to specify `--parallel-threads=auto`,
+`pytest.mark.force_parallel_threads("auto")`, or
+`pytest.mark.parallel_threads_limit("auto")` which will let
 `pytest-run-parallel` choose the number of logical CPU cores available
 to the testing process. If that cannot be determined, the number of
 physical CPU cores will be used. If that fails as well, it will fall
@@ -260,7 +266,7 @@ Note that using `pytest-xdist` and setting `iterations` to a number
 greater than one might cause tests to run even more times than intended.
 
 The other mode of operation occurs at the individual test level, via the
-`pytest.mark.parallel_threads` and `pytest.mark.iterations` markers:
+`pytest.mark.force_parallel_threads` and `pytest.mark.iterations` markers:
 
 ```python
 # test_file.py
@@ -270,15 +276,15 @@ import pytest
 def my_fixture():
     ...
 
-@pytest.mark.parallel_threads(2)
+@pytest.mark.force_parallel_threads(2)
 @pytest.mark.iterations(10)
 def test_something_1():
     # This test will be run in parallel using two concurrent threads
     # and 10 times in each thread
     ...
 
 @pytest.mark.parametrize('arg', [1, 2, 3])
-@pytest.mark.parallel_threads(3)
+@pytest.mark.force_parallel_threads(3)
 def test_fixture(my_fixture, arg):
     # pytest markers and fixtures are supported as well
     ...

src/pytest_run_parallel/plugin.py

@@ -436,16 +436,22 @@ def pytest_configure(config):
     config.addinivalue_line(
         "markers",
         "parallel_threads(n): run the given test function in parallel "
-        "using `n` threads. Note that if n is greater than 1, the test "
-        "run with this many threads even if the --parallel-threads "
-        "command-line argument is not passed. Use parallel_threads_limit "
-        "instead if you want to avoid this pitfall.",
+        "using `n` threads. Deprecated if `n` is greater than 1. Use either "
+        "the parallel_threads_limit or force_parallel_threads marker to make "
+        "your intention clearer.",
     )
     config.addinivalue_line(
         "markers",
         "parallel_threads_limit(n): run the given test function in parallel "
         "using a maximum of `n` threads.",
     )
+    config.addinivalue_line(
+        "markers",
+        "force_parallel_threads(n): force the given test function to run in "
+        "parallel using `n` threads, overriding the --parallel-threads "
+        "command-line argument and any parallel_threads_limit marker. Use "
+        "this to ensure a test always runs with a specific number of threads.",
+    )
     config.addinivalue_line(
         "markers",
         "iterations(n): run the given test function `n` times in each thread",

src/pytest_run_parallel/utils.py

@@ -22,15 +22,16 @@ def auto_or_int(val):
 
 def get_num_workers(item):
     n_workers = get_configured_num_workers(item.config)
-    # TODO: deprecate in favor of parallel_threads_limit
     marker_used = False
     marker = item.get_closest_marker("parallel_threads")
     if marker is not None:
         marker_used = True
         n_workers = auto_or_int(marker.args[0])
         if n_workers > 1:
             warnings.warn(
-                "Using the parallel_threads marker with a value greater than 1 is deprecated. Use parallel_threads_limit instead.",
+                "Using the parallel_threads marker with a value greater than 1 is deprecated. "
+                "Use parallel_threads_limit if you want to set a thread limit or "
+                "force_parallel_threads if you want to force a test to be multithreaded.",
                 DeprecationWarning,
                 stacklevel=2,
             )
@@ -42,6 +43,12 @@ def get_num_workers(item):
         if n_workers > val:
             n_workers = val
 
+    force_marker = item.get_closest_marker("force_parallel_threads")
+    if force_marker is not None:
+        n_workers = auto_or_int(force_marker.args[0])
+        if n_workers == 1:
+            marker_used = True
+
     return n_workers, marker_used
 
 

tests/test_run_parallel.py

@@ -846,6 +846,92 @@ def test_parallel_threads_two():
     )
 
 
+def test_force_parallel_threads_marker(pytester):
+    pytester.makepyfile("""
+        import pytest
+
+        def test_default_threads(num_parallel_threads):
+            assert num_parallel_threads == 1
+
+        @pytest.mark.force_parallel_threads(4)
+        def test_forced_four(num_parallel_threads):
+            assert num_parallel_threads == 4
+
+        @pytest.mark.force_parallel_threads(1)
+        def test_forced_one(num_parallel_threads):
+            assert num_parallel_threads == 1
+    """)
+
+    result = pytester.runpytest("-v")
+    assert result.ret == 0
+    result.stdout.fnmatch_lines(
+        [
+            "*::test_default_threads PASSED*",
+            "*::test_forced_four PARALLEL PASSED*",
+            "*::test_forced_one PASSED*",
+        ]
+    )
+
+
+def test_force_parallel_threads_overrides_cli(pytester):
+    pytester.makepyfile("""
+        import pytest
+
+        def test_uses_cli(num_parallel_threads):
+            assert num_parallel_threads == 10
+
+        @pytest.mark.force_parallel_threads(3)
+        def test_forced_overrides_cli(num_parallel_threads):
+            assert num_parallel_threads == 3
+    """)
+
+    result = pytester.runpytest("--parallel-threads=10", "-v")
+    assert result.ret == 0
+    result.stdout.fnmatch_lines(
+        [
+            "*::test_uses_cli PARALLEL PASSED*",
+            "*::test_forced_overrides_cli PARALLEL PASSED*",
+        ]
+    )
+
+
+def test_force_parallel_threads_overrides_limit(pytester):
+    pytester.makepyfile("""
+        import pytest
+
+        @pytest.mark.force_parallel_threads(5)
+        @pytest.mark.parallel_threads_limit(2)
+        def test_force_beats_limit(num_parallel_threads):
+            assert num_parallel_threads == 5
+    """)
+
+    result = pytester.runpytest("--parallel-threads=10", "-v")
+    assert result.ret == 0
+    result.stdout.fnmatch_lines(
+        [
+            "*::test_force_beats_limit PARALLEL PASSED*",
+        ]
+    )
+
+
+def test_force_parallel_threads_no_deprecation_warning(pytester):
+    pytester.makepyfile("""
+        import pytest
+
+        @pytest.mark.force_parallel_threads(3)
+        def test_no_warning():
+            assert True
+    """)
+
+    result = pytester.runpytest("-v", "-W", "error::DeprecationWarning")
+    assert result.ret == 0
+    result.stdout.fnmatch_lines(
+        [
+            "*::test_no_warning PARALLEL PASSED*",
+        ]
+    )
+
+
 def test_forever_without_selected_tests(pytester):
     pytester.makepyfile("")
     result = pytester.runpytest("--forever", "-v")