Support testing np and tnp on the same test

torch_np/tests/conftest.py

@@ -2,6 +2,8 @@
 
 import pytest
 
+import torch_np as tnp
+
 
 def pytest_configure(config):
     config.addinivalue_line("markers", "slow: very slow tests")
@@ -12,14 +14,59 @@ def pytest_addoption(parser):
     parser.addoption("--nonp", action="store_true", help="error when NumPy is accessed")
 
 
+class Inaccessible:
+    def __getattribute__(self, attr):
+        raise RuntimeError(f"Using --nonp but accessed np.{attr}")
+
+
 def pytest_sessionstart(session):
     if session.config.getoption("--nonp"):
+        sys.modules["numpy"] = Inaccessible()
 
-        class Inaccessible:
-            def __getattribute__(self, attr):
-                raise RuntimeError(f"Using --nonp but accessed np.{attr}")
 
-        sys.modules["numpy"] = Inaccessible()
+def pytest_generate_tests(metafunc):
+    """
+    Hook to parametrize test cases
+    See https://docs.pytest.org/en/6.2.x/parametrize.html#pytest-generate-tests
+
+    The logic here allows us to test with both NumPy-proper and torch_np.
+    Normally we'd just test torch_np, e.g.
+
+        import torch_np as np
+        ...
+        def test_foo():
+            np.array([42])
+            ...
+
+    but this hook allows us to test NumPy-proper as well, e.g.
+
+        def test_foo(np):
+            np.array([42])
+            ...
+
+    np is a pytest parameter, which is either NumPy-proper or torch_np. This
+    allows us to sanity check our own tests, so that tested behaviour is
+    consistent with NumPy-proper.
+
+    pytest will have test names respective to the library being tested, e.g.
+
+        $ pytest --collect-only
+        test_foo[torch_np]
+        test_foo[numpy]
+
+    """
+    np_params = [tnp]
+
+    try:
+        import numpy as np
+    except ImportError:
+        pass
+    else:
+        if not isinstance(np, Inaccessible):  # i.e. --nonp was used
+            np_params.append(np)
+
+    if "np" in metafunc.fixturenames:
+        metafunc.parametrize("np", np_params)
 
 
 def pytest_collection_modifyitems(config, items):