Merge pull request numpy#25999 from mattip/assert_warns

BUG: fix kwarg handling in assert_warn [skip cirrus][skip azp]

Author: charris

numpy/testing/_private/utils.py

@@ -1949,8 +1949,15 @@ def assert_warns(warning_class, *args, **kwargs):
     >>> ret = np.testing.assert_warns(DeprecationWarning, deprecated_func, 4)
     >>> assert ret == 16
     """
-    if not args:
+    if not args and not kwargs:
         return _assert_warns_context(warning_class)
+    elif len(args) < 1:
+        if "match" in kwargs:
+            raise RuntimeError(
+                "assert_warns does not use 'match' kwarg, "
+                "use pytest.warns instead"
+                )
+        raise RuntimeError("assert_warns(...) needs at least one arg")
 
     func = args[0]
     args = args[1:]

numpy/testing/tests/test_utils.py

@@ -1035,6 +1035,27 @@ def no_warnings():
         assert_equal(before_filters, after_filters,
                      "assert_warns does not preserver warnings state")
 
+    def test_args(self):
+        def f(a=0, b=1):
+            warnings.warn("yo")
+            return a + b
+
+        assert assert_warns(UserWarning, f, b=20) == 20
+
+        with pytest.raises(RuntimeError) as exc:
+            # assert_warns cannot do regexp matching, use pytest.warns
+            with assert_warns(UserWarning, match="A"):
+                warnings.warn("B", UserWarning)
+        assert "assert_warns" in str(exc)
+        assert "pytest.warns" in str(exc)
+
+        with pytest.raises(RuntimeError) as exc:
+            # assert_warns cannot do regexp matching, use pytest.warns
+            with assert_warns(UserWarning, wrong="A"):
+                warnings.warn("B", UserWarning)
+        assert "assert_warns" in str(exc)
+        assert "pytest.warns" not in str(exc)
+
     def test_warn_wrong_warning(self):
         def f():
             warnings.warn("yo", DeprecationWarning)