tests: fix test_memusage_partial_open and add psutil to CI

Run the RSS measurement in a subprocess so the fixture file is not
already in the page cache from earlier tests (which made both deltas
read as zero). Add psutil to the CI pip install so this test is not
skipped there.

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.github/workflows/ci.yml

@@ -55,7 +55,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install xmlschema xsdata numpy lxml pytest isodate lark networkx tabulate python-dateutil shapely
+          pip install xmlschema xsdata numpy lxml pytest isodate lark networkx tabulate python-dateutil shapely psutil
           pip install src/bcf --no-deps
           pip install pytest-xdist==3.8.0
 

src/ifcopenshell-python/test/test_streaming_rocksdb_and_simpletyperefs.py

@@ -74,14 +74,29 @@ def test_opening_unicode():
 
 @pytest.mark.skipif(psutil is None, reason="psutil not installed")
 def test_memusage_partial_open():
-    m0 = psutil.Process().memory_info().rss
-    f = ifcopenshell.open(fn)
-    m1 = psutil.Process().memory_info().rss
-    g = ifcopenshell.open(fn, bypass_types=("IfcRepresentationItem",))
-    m2 = psutil.Process().memory_info().rss
-    # arbitrary...
-    expected_ratio = 0.75
-    assert (m2 - m1) < (m1 - m0) * expected_ratio
+    # Run in a subprocess to ensure the file is not already in the process page
+    # cache from earlier tests, which would make both RSS deltas read as zero.
+    import subprocess
+    import sys
+
+    script = f"""
+import psutil
+import ifcopenshell
+
+fn = {repr(fn)}
+m0 = psutil.Process().memory_info().rss
+f = ifcopenshell.open(fn)
+m1 = psutil.Process().memory_info().rss
+g = ifcopenshell.open(fn, bypass_types=("IfcRepresentationItem",))
+m2 = psutil.Process().memory_info().rss
+expected_ratio = 0.75
+assert (m2 - m1) < (m1 - m0) * expected_ratio, (
+    f"bypass_types did not reduce memory: normal open added {{m1 - m0}} bytes, "
+    f"bypass open added {{m2 - m1}} bytes (expected < {{(m1 - m0) * expected_ratio:.0f}})"
+)
+"""
+    result = subprocess.run([sys.executable, "-c", script], capture_output=True, text=True)
+    assert result.returncode == 0, result.stderr or result.stdout
 
 
 def test_rocks():