Add a regression test for lazy imports

lumicks/pylake/tests/test_import_time.py

@@ -1,3 +1,4 @@
+import ast
 import sys
 import subprocess
 from textwrap import dedent
@@ -26,3 +27,33 @@ def test_disabling_capturing(report_line):
     report_line(
         f"Module import time: {np.mean(times):.2f} +- {np.std(times):.2f} seconds (N={repeats})"
     )
+
+
+def test_lazy_imports():
+    """Ensure that specific third-party modules are lazily imported so that `pylake` stays fast"""
+
+    expected_lazy_imports = [
+        "h5py",
+        "sklearn",
+        "matplotlib",
+        "scipy.stats",
+        "scipy.signal",
+        "scipy.ndimage",
+        "scipy.special",
+        "scipy.optimize",
+        "scipy.interpolate",
+    ]
+
+    # `sys.modules` in this new Python process will only contain what `pylake` imports
+    code = dedent(
+        """\
+        import sys
+        import lumicks.pylake
+        print(list(sys.modules.keys()))
+        """
+    )
+    output = subprocess.check_output([sys.executable, "-c", code], text=True)
+
+    imported_modules = ast.literal_eval(output)
+    for lazy_import in expected_lazy_imports:
+        assert not any(lazy_import in m for m in imported_modules)