2 files changed, 59 insertions, 3 deletions
diff --git a/doc/release/upcoming_changes/XXXXXX.compatibility.rst b/doc/release/upcoming_changes/XXXXXX.compatibility.rst
deleted file mode 100644
index 565d114a1..000000000
--- a/doc/release/upcoming_changes/XXXXXX.compatibility.rst
+++ /dev/null
@@ -1,3 +0,0 @@
-* `PyArray_CanCastArrayTo` does NOT honor the warning request.
-  Potential alternative: Honor it, but not if the warning is
-  raised (because it swallows errors :().
diff --git a/numpy/core/tests/test_nep50_promotions.py b/numpy/core/tests/test_nep50_promotions.py
new file mode 100644
index 000000000..1f06beb93
--- /dev/null
+++ b/numpy/core/tests/test_nep50_promotions.py
@@ -0,0 +1,59 @@
+"""
+This file adds basic tests to test the NEP 50 style promotion compatibility
+mode.  Most of these test are likely to be simply deleted again once NEP 50
+is adopted in the main test suite.  A few may be moved elsewhere.
+"""
+
+import numpy as np
+import pytest
+
+
+@pytest.fixture(scope="module", autouse=True)
+def _weak_promotion_enabled():
+    state = np._get_promotion_state()
+    np._set_promotion_state("weak_and_warn")
+    yield
+    np._set_promotion_state(state)
+
+
+def test_nep50_examples():
+    with pytest.warns(UserWarning, match="result dtype changed"):
+        res = np.uint8(1) + 2
+    assert res.dtype == np.uint8
+
+    with pytest.warns(UserWarning, match="result dtype changed"):
+        res = np.array([1], np.uint8) + np.int64(1)
+    assert res.dtype == np.int64
+
+    with pytest.warns(UserWarning, match="result dtype changed"):
+        res = np.array([1], np.uint8) + np.array(1, dtype=np.int64)
+    assert res.dtype == np.int64
+
+    # Note: The following should warn due to overflow (depends gh-21437)
+    with pytest.warns(UserWarning, match="result dtype changed"):
+        res = np.float32(1) + 3e100
+    assert np.isinf(res)
+
+    # Changes, but we don't warn for it (too noisy)
+    res = np.array([0.1], np.float32) == np.float64(0.1)
+    assert res[0] == False
+
+    # Additional test, since the above silences the warning:
+    with pytest.warns(UserWarning, match="result dtype changed"):
+        res = np.array([0.1], np.float32) + np.float64(0.1)
+    assert res.dtype == np.float64
+
+    with pytest.warns(UserWarning, match="result dtype changed"):
+        res = np.array([1.], np.float32) + np.int64(3)
+    assert res.dtype == np.float64
+
+
+@pytest.mark.xfail
+def test_nep50_integer_conversion_errors():
+    # Implementation for error paths is mostly missing (as of writing)
+    with pytest.raises(ValueError):  # (or TypeError?)
+        np.array([1], np.uint8) + 300
+
+    with pytest.raises(ValueError):  # (or TypeError?)
+        np.uint8(1) + 300
+