Merge pull request #178 from ngoldbaum/fix-single-core

Author: ngoldbaum

.github/workflows/main.yml

@@ -51,3 +51,27 @@ jobs:
       - name: Check manifest
         run: |
           check-manifest -u -v
+
+  test-single-cpu:
+    runs-on: ubuntu-latest
+    name: Run tests on a simulated single-CPU system
+    steps:
+      - uses: actions/checkout@v5
+      - uses: actions/setup-python@v6
+        with:
+          python-version: '3.14'
+
+      - name: Setup uv
+        uses: astral-sh/setup-uv@v7
+        with:
+          activate-environment: true
+
+      - name: Install dependencies
+        run: |
+          uv sync --locked --group test
+
+      - name: Run tests pinned to a single CPU
+        # Regression coverage for issue #177: --parallel-threads=auto must
+        # degrade gracefully when only one CPU is available.
+        run: |
+          taskset -c 0 python -m pytest tests/

MANIFEST.in

@@ -1,4 +1,4 @@
-include tests/conftest.py
+recursive-include tests *.py
 exclude pytest_run_parallel.egg-info
 recursive-exclude * *.egg-info
 recursive-include docs *.bat

tests/_helpers.py

@@ -0,0 +1,12 @@
+from pytest_run_parallel.cpu_detection import get_logical_cpus
+
+
+def passing_status(threads):
+    # Pytest reports "PARALLEL PASSED" only when the resolved worker count is
+    # greater than 1. On single-CPU systems --parallel-threads=auto resolves
+    # to 1, so the status degrades to "PASSED" (issue #177).
+    if threads == "auto":
+        n = get_logical_cpus() or 1
+    else:
+        n = int(threads)
+    return "PARALLEL PASSED" if n > 1 else "PASSED"

tests/test_cpu_detection.py

@@ -158,3 +158,50 @@ def test_auto_detect_cpus(num_parallel_threads):
             "*::test_auto_detect_cpus PARALLEL PASSED*",
         ]
     )
+
+
+def test_auto_detect_single_cpu(
+    pytester: pytest.Pytester, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    # Regression test for issue #177: on a single-CPU system,
+    # --parallel-threads=auto must degrade gracefully to 1 thread without
+    # erroring out, and tests should still run (just sequentially).
+    monkeypatch.setattr("pytest_run_parallel.utils.get_logical_cpus", lambda: 1)
+
+    pytester.makepyfile("""
+        def test_single_cpu(num_parallel_threads):
+            assert num_parallel_threads == 1
+    """)
+
+    result = pytester.runpytest("--parallel-threads=auto", "-v")
+
+    result.stdout.fnmatch_lines(
+        [
+            "*::test_single_cpu PASSED*",
+        ]
+    )
+    assert "PARALLEL PASSED" not in result.stdout.str()
+    assert result.ret == 0
+
+
+def test_auto_detect_no_cpu_info(
+    pytester: pytest.Pytester, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    # Regression test for issue #177: when every CPU-detection path returns
+    # None, --parallel-threads=auto must still fall back to 1 rather than
+    # crashing.
+    monkeypatch.setattr("pytest_run_parallel.utils.get_logical_cpus", lambda: None)
+
+    pytester.makepyfile("""
+        def test_no_cpu_info(num_parallel_threads):
+            assert num_parallel_threads == 1
+    """)
+
+    result = pytester.runpytest("--parallel-threads=auto", "-v")
+
+    result.stdout.fnmatch_lines(
+        [
+            "*::test_no_cpu_info PASSED*",
+        ]
+    )
+    assert result.ret == 0

tests/test_thread_index.py

@@ -1,4 +1,7 @@
 import pytest
+from _helpers import passing_status
+
+from pytest_run_parallel.cpu_detection import get_logical_cpus
 
 
 def test_thread_index_single_thread(pytester: pytest.Pytester) -> None:
@@ -26,12 +29,15 @@ def test_thread_index(thread_index, num_parallel_threads):
 
     result.stdout.fnmatch_lines(
         [
-            "*::test_thread_index PARALLEL PASSED*",
+            f"*::test_thread_index {passing_status('auto')}*",
         ]
     )
 
 
 def test_thread_index_changes_between_tests(pytester: pytest.Pytester) -> None:
+    if (get_logical_cpus() or 1) < 2:
+        pytest.skip("requires more than one CPU to compare thread indexes")
+
     # thread_comp is checking if the thread_indexes are equal between threads.
     # should fail since thread_indexes should not match.
     # test can be improved, since this cannot check if every thread has a
@@ -60,7 +66,7 @@ def test_iteration_index(iteration_index):
 
     result.stdout.fnmatch_lines(
         [
-            "*::test_iteration_index PARALLEL PASSED*",
+            f"*::test_iteration_index {passing_status('auto')}*",
         ]
     )
 
@@ -92,6 +98,6 @@ def test_iteration_index(iteration_index, num_iterations):
 
     result.stdout.fnmatch_lines(
         [
-            "*::test_iteration_index PARALLEL PASSED*",
+            f"*::test_iteration_index {passing_status('auto')}*",
         ]
     )

tests/test_tmp_path.py

@@ -1,13 +1,11 @@
 import pytest
+from _helpers import passing_status
 
-parallel_threads = [
-    (1, "PASSED"),  # no parallel threads
-    ("auto", "PARALLEL PASSED"),  # parallel threads
-]
+parallel_threads = [1, "auto"]
 
 
-@pytest.mark.parametrize("parallel, passing", parallel_threads)
-def test_tmp_path_is_empty(pytester: pytest.Pytester, parallel, passing):
+@pytest.mark.parametrize("parallel", parallel_threads)
+def test_tmp_path_is_empty(pytester: pytest.Pytester, parallel):
     # ensures tmp_path is empty for each thread
     # test from (gh-109)
     pytester.makepyfile("""
@@ -26,13 +24,13 @@ def test_tmp_path(tmp_path):
 
     result.stdout.fnmatch_lines(
         [
-            f"*::test_tmp_path {passing}*",
+            f"*::test_tmp_path {passing_status(parallel)}*",
         ]
     )
 
 
-@pytest.mark.parametrize("parallel, passing", parallel_threads)
-def test_tmp_path_read_write(pytester: pytest.Pytester, parallel, passing):
+@pytest.mark.parametrize("parallel", parallel_threads)
+def test_tmp_path_read_write(pytester: pytest.Pytester, parallel):
     # ensures we can read/write in each tmp_path
     pytester.makepyfile("""
         def test_tmp_path(tmp_path):
@@ -47,13 +45,13 @@ def test_tmp_path(tmp_path):
 
     result.stdout.fnmatch_lines(
         [
-            f"*::test_tmp_path {passing}*",
+            f"*::test_tmp_path {passing_status(parallel)}*",
         ]
     )
 
 
-@pytest.mark.parametrize("parallel, passing", parallel_threads)
-def test_tmp_path_delete(pytester: pytest.Pytester, parallel, passing):
+@pytest.mark.parametrize("parallel", parallel_threads)
+def test_tmp_path_delete(pytester: pytest.Pytester, parallel):
     # ensures we can delete files in each tmp_path
     pytester.makepyfile("""
         def test_tmp_path(tmp_path):
@@ -73,13 +71,13 @@ def test_tmp_path(tmp_path):
 
     result.stdout.fnmatch_lines(
         [
-            f"*::test_tmp_path {passing}*",
+            f"*::test_tmp_path {passing_status(parallel)}*",
         ]
     )
 
 
-@pytest.mark.parametrize("parallel, passing", parallel_threads)
-def test_tmpdir_is_empty(pytester: pytest.Pytester, parallel, passing):
+@pytest.mark.parametrize("parallel", parallel_threads)
+def test_tmpdir_is_empty(pytester: pytest.Pytester, parallel):
     # ensures tmpdir is empty for each thread
     pytester.makepyfile("""
         def test_tmpdir(tmpdir):
@@ -94,13 +92,13 @@ def test_tmpdir(tmpdir):
 
     result.stdout.fnmatch_lines(
         [
-            f"*::test_tmpdir {passing}*",
+            f"*::test_tmpdir {passing_status(parallel)}*",
         ]
     )
 
 
-@pytest.mark.parametrize("parallel, passing", parallel_threads)
-def test_tmpdir_read_write(pytester: pytest.Pytester, parallel, passing):
+@pytest.mark.parametrize("parallel", parallel_threads)
+def test_tmpdir_read_write(pytester: pytest.Pytester, parallel):
     # ensures we can read/write in each tmpdir
     pytester.makepyfile("""
         def test_tmpdir(tmpdir):
@@ -115,13 +113,13 @@ def test_tmpdir(tmpdir):
 
     result.stdout.fnmatch_lines(
         [
-            f"*::test_tmpdir {passing}*",
+            f"*::test_tmpdir {passing_status(parallel)}*",
         ]
     )
 
 
-@pytest.mark.parametrize("parallel, passing", parallel_threads)
-def test_tmpdir_delete(pytester: pytest.Pytester, parallel, passing):
+@pytest.mark.parametrize("parallel", parallel_threads)
+def test_tmpdir_delete(pytester: pytest.Pytester, parallel):
     # ensures we can delete files in each tmpdir
     pytester.makepyfile("""
         def test_tmpdir(tmpdir):
@@ -140,13 +138,13 @@ def test_tmpdir(tmpdir):
 
     result.stdout.fnmatch_lines(
         [
-            f"*::test_tmpdir {passing}*",
+            f"*::test_tmpdir {passing_status(parallel)}*",
         ]
     )
 
 
-@pytest.mark.parametrize("parallel, passing", parallel_threads)
-def test_tmp_path_tmpdir(pytester: pytest.Pytester, parallel, passing):
+@pytest.mark.parametrize("parallel", parallel_threads)
+def test_tmp_path_tmpdir(pytester: pytest.Pytester, parallel):
     # ensures tmp_path and tmpdir can be used at the same time
     pytester.makepyfile("""
         def test_both(tmp_path, tmpdir):
@@ -159,6 +157,6 @@ def test_both(tmp_path, tmpdir):
 
     result.stdout.fnmatch_lines(
         [
-            f"*::test_both {passing}*",
+            f"*::test_both {passing_status(parallel)}*",
         ]
     )