Modified validation for expected exceptions and warnings in pytest APIs

src/_pytest/mark/structures.py

@@ -426,9 +426,24 @@ def __call__(
             *conditions: Union[str, bool],
             reason: str = ...,
             run: bool = ...,
-            raises: Union[Type[BaseException], Tuple[Type[BaseException], ...]] = ...,
+            raises: Union[Type[BaseException], Tuple[Type[BaseException], ...]] = (),
             strict: bool = ...,
         ) -> MarkDecorator:
+            __tracebackhide__ = True
+            if raises is None:
+                raise UsageError(
+                    "Passing `raises=None` to xfail is an error, because it's "
+                    "impossible to raise an exception which is not an instance of any type. "
+                    "Raising exceptions is already understood as failing the test, so you "
+                    "don't need any special code to say 'this should never raise an exception'."
+                )
+            elif isinstance(raises, tuple) and not raises:
+                raise UsageError(
+                    "Passing `raises=()` to xfail is an error, because it's impossible "
+                    "to raise an exception which is not an instance of any type. Raising "
+                    "exceptions is already understood as failing the test, so you don't need "
+                    "any special code to say 'this should never raise an exception'."
+                )
             ...
 
     class _ParametrizeMarkDecorator(MarkDecorator):

src/_pytest/python_api.py

@@ -708,6 +708,19 @@ def approx(expected, rel=None, abs=None, nan_ok: bool = False) -> ApproxBase:
 
     __tracebackhide__ = True
 
+    if expected_exception is None:
+        raise UsageError(
+            "Passing `expected_exception=None` is invalid, as it is ambiguous for "
+            "what exceptions pytest should catch. To assert that no exception is "
+            "expected, simply execute the block without using `pytest.raises()`."
+        )
+    if isinstance(expected_exception, tuple) and not expected_exception:
+        raise UsageError(
+            "Passing an empty tuple `expected_exception=()` is invalid, as it would "
+            "not specify any exceptions to catch. To assert that no exception is "
+            "expected, simply execute the block without using `pytest.raises()`."
+        )
+
     if isinstance(expected, Decimal):
         cls: Type[ApproxBase] = ApproxDecimal
     elif isinstance(expected, Mapping):

src/_pytest/recwarn.py

@@ -78,6 +78,20 @@ def deprecated_call(
     one for each warning raised.
     """
     __tracebackhide__ = True
+    if expected_warning is None:
+        raise TypeError(
+            "Passing `expected_warning=None` is an error, because it's "
+            "impossible to emit a warning which is not an instance of any type. "
+            "To assert that no warnings are emitted, use `pytest.warns(None)` to explicitly "
+            "declare that no warnings are expected."
+        )
+    elif isinstance(expected_warning, tuple) and not expected_warning:
+        raise TypeError(
+            "Passing `expected_warning=()` is an error, because it's "
+            "impossible to emit a warning which is not an instance of any type. "
+            "To assert that no warnings are emitted, use `pytest.warns(None)` to explicitly "
+            "declare that no warnings are expected."
+        )
     if func is not None:
         args = (func,) + args
     return warns((DeprecationWarning, PendingDeprecationWarning), *args, **kwargs)