Racing condition xdist fix (#273)

* minor fixes

* isolate tmp files in workers

* Update ultraplot/tests/conftest.py

Co-authored-by: Copilot <[email protected]>

---------

Co-authored-by: Copilot <[email protected]>

Author: cvanelteren

ultraplot/tests/conftest.py

@@ -54,6 +54,50 @@ def test_something(rng):
     return np.random.default_rng(seed=SEED)
 
 
+@pytest.fixture(autouse=True)
+def isolate_mpl_testing():
+    """
+    Isolate matplotlib testing for parallel execution.
+
+    This prevents race conditions in parallel testing (pytest-xdist) where
+    multiple processes can interfere with each other's image comparison tests.
+    The main issue is that pytest-mpl uses shared temporary directories that
+    can conflict between processes.
+    """
+    import matplotlib as mpl
+    import matplotlib.pyplot as plt
+    import tempfile
+    import os
+
+    # Store original backend and ensure consistent state
+    original_backend = mpl.get_backend()
+    if original_backend != "Agg":
+        mpl.use("Agg", force=True)
+
+    # Clear any existing figures
+    plt.close("all")
+
+    # Create process-specific temporary directory for mpl results
+    # This prevents file conflicts between parallel processes
+    worker_id = os.environ.get("PYTEST_XDIST_WORKER", "master")
+    with tempfile.TemporaryDirectory(prefix=f"mpl_test_{worker_id}_") as temp_dir:
+        os.environ["MPL_TEST_TEMP_DIR"] = temp_dir
+
+        yield
+
+    # Clean up after test
+    plt.close("all")
+    uplt.close("all")
+
+    # Remove environment variable
+    if "MPL_TEST_TEMP_DIR" in os.environ:
+        del os.environ["MPL_TEST_TEMP_DIR"]
+
+    # Restore original backend
+    if original_backend != "Agg":
+        mpl.use(original_backend, force=True)
+
+
 @pytest.fixture(autouse=True)
 def close_figures_after_test():
     """Automatically close all figures after each test."""
@@ -139,11 +183,20 @@ def pytest_configure(config):
     - Suppresses verbose matplotlib logging
     - Registers the StoreFailedMplPlugin for enhanced functionality
     - Sets up the plugin regardless of cleanup options (HTML reports always available)
+    - Configures process-specific temporary directories for parallel testing
     """
     # Suppress ultraplot config loading which mpl does not recognize
     logging.getLogger("matplotlib").setLevel(logging.ERROR)
     logging.getLogger("ultraplot").setLevel(logging.WARNING)
 
+    # Configure process-specific results directory for parallel testing
+    worker_id = os.environ.get("PYTEST_XDIST_WORKER", "master")
+    if (
+        not hasattr(config.option, "mpl_results_path")
+        or not config.option.mpl_results_path
+    ):
+        config.option.mpl_results_path = f"./mpl-results-{worker_id}"
+
     try:
         # Always register the plugin - it provides enhanced functionality beyond just cleanup
         config.pluginmanager.register(StoreFailedMplPlugin(config))

ultraplot/tests/test_1dplots.py

@@ -525,7 +525,7 @@ def test_heatmap_labels(rng):
     return fig
 
 
-@pytest.mark.mpl_image_compare()
+@pytest.mark.mpl_image_compare
 def test_networks(rng):
     """
     Create a baseline network graph that tests
@@ -575,7 +575,7 @@ def test_networks(rng):
         inax = ax.inset_axes([*pos, 0.2, 0.2], zoom=0)
         layout_kw = {}
         if layout in ("random", "spring", "arf"):
-            layout_kw = dict(seed=SEED)
+            layout_kw = dict(seed=np.random.default_rng(SEED))
 
         inax.graph(
             g,