update test_build for robustness

Summary: Change cyclic deps test to be independent of test discovery order. Also let it work without plotly.

Reviewed By: nikhilaravi

Differential Revision: D30669614

fbshipit-source-id: 2eadf3f8b56b6096c5466ce53b4f8ac6df27b964

tests/test_build.py

@@ -118,14 +118,16 @@ class TestBuild(unittest.TestCase):
         # Check each module of pytorch3d imports cleanly,
         # which may fail if there are import cycles.
 
-        # First check the setup of the test. If any of pytorch3d
-        # was already imported the test would be pointless.
-        for module in sys.modules:
-            self.assertFalse(module.startswith("pytorch3d"), module)
+        with unittest.mock.patch.dict(sys.modules):
+            for module in list(sys.modules):
+                # If any of pytorch3d is already imported,
+                # the test would be pointless.
+                if module.startswith("pytorch3d"):
+                    sys.modules.pop(module, None)
 
             root_dir = get_pytorch3d_dir() / "pytorch3d"
             for module_file in root_dir.glob("**/*.py"):
-            if module_file.stem == "__init__":
+                if module_file.stem in ("__init__", "plotly_vis"):
                     continue
                 relative_module = str(module_file.relative_to(root_dir))[:-3]
                 module = "pytorch3d." + relative_module.replace("/", ".")