Add a test for lazy module loading

mdboom · mdboom · commit cae5a92dee30 · 2018-11-08T22:01:46.000-05:00
diff --git a/lib/matplotlib/tests/test_basic.py b/lib/matplotlib/tests/test_basic.py
@@ -1,8 +1,11 @@
 import builtins
+import subprocess
+import sys
 
 import matplotlib
 
 
+
 def test_simple():
     assert 1 + 1 == 2
 
@@ -34,3 +37,38 @@ def test_override_builtins():
 
 def test_verbose():
     assert isinstance(matplotlib.verbose, matplotlib.Verbose)
+
+
+def test_lazy_imports():
+    # The list of modules we want to ensure aren't imported by default
+    lazy_modules = [
+        'matplotlib._png',
+        'matplotlib._tri',
+        'matplotlib._qhull',
+        'matplotlib._contour'
+    ]
+
+    # The list of modules to import that shouldn't import any of the
+    # lazy_modules
+    top_level_modules = [
+        'matplotlib.figure',
+        'matplotlib.backend_bases',
+        'matplotlib.pyplot'
+    ]
+
+    for top_level_module in top_level_modules:
+        lines = [
+            "import sys",
+            "import {}".format(top_level_module)
+        ]
+        for lazy_module in lazy_modules:
+            lines.append('assert {!r} not in sys.modules'.format(lazy_module))
+        source = '\n'.join(lines)
+
+        print(source)
+
+        subprocess.check_call([
+            sys.executable,
+            '-c',
+            source
+        ])
