B017: don't warn when pytest.raises() has a match argument

Fix PyCQA#334 .

Also add more tests for when we should and shouldn't emit B017.
In particular we should check ``assertRaises`` and ``pytest.raises``
calls outside of with statements.

README.rst

@@ -127,12 +127,13 @@ waste CPU instructions. Either prepend ``assert`` or remove it.
 **B016**: Cannot raise a literal. Did you intend to return it or raise
 an Exception?
 
-**B017**: ``self.assertRaises(Exception):`` should be considered evil. It can lead
-to your test passing even if the code being tested is never executed due to a typo.
-Either assert for a more specific exception (builtin or custom), use
-``assertRaisesRegex``, or use the context manager form of assertRaises
-(``with self.assertRaises(Exception) as ex:``) with an assertion against the
-data available in ``ex``.
+**B017**: ``assertRaises(Exception)`` and ``pytest.raises(Exception)`` should
+be considered evil. They can lead to your test passing even if the
+code being tested is never executed due to a typo. Assert for a more
+specific exception (builtin or custom), or use ``assertRaisesRegex``
+(if using ``assertRaises``), or add the ``match`` keyword argument (if
+using ``pytest.raises``), or use the context manager form with a target
+(e.g. ``with self.assertRaises(Exception) as ex:``).
 
 **B018**: Found useless expression. Either assign it to a variable or remove it.
 

bugbear.py

@@ -534,16 +534,14 @@ def check_for_b017(self, node):
 
         if (
             hasattr(item_context, "func")
+            and isinstance(item_context.func, ast.Attribute)
             and (
-                (
-                    hasattr(item_context.func, "attr")
-                    and item_context.func.attr == "assertRaises"
-                )
+                item_context.func.attr == "assertRaises"
                 or (
-                    isinstance(item_context.func, ast.Attribute)
-                    and item_context.func.attr == "raises"
+                    item_context.func.attr == "raises"
                     and isinstance(item_context.func.value, ast.Name)
                     and item_context.func.value.id == "pytest"
+                    and "match" not in [kwd.arg for kwd in item_context.keywords]
                 )
             )
             and len(item_context.args) == 1
@@ -1411,11 +1409,12 @@ def visit_Lambda(self, node):
 )
 B017 = Error(
     message=(
-        "B017 assertRaises(Exception): or pytest.raises(Exception) should "
-        "be considered evil. It can lead to your test passing even if the "
-        "code being tested is never executed due to a typo. Either assert "
-        "for a more specific exception (builtin or custom), use "
-        "assertRaisesRegex, or use the context manager form of assertRaises."
+        "B017 `assertRaises(Exception)` and `pytest.raises(Exception)` should "
+        "be considered evil. They can lead to your test passing even if the "
+        "code being tested is never executed due to a typo. Assert for a more "
+        "specific exception (builtin or custom), or use `assertRaisesRegex` "
+        "(if using `assertRaises`), or add the `match` keyword argument (if "
+        "using `pytest.raises`), or use the context manager form with a target."
     )
 )
 B018 = Error(

tests/b017.py

@@ -1,6 +1,6 @@
 """
 Should emit:
-B017 - on lines 24 and 26.
+B017 - on lines 24, 26, 28, 31 and 32.
 """
 import asyncio
 import unittest
@@ -23,8 +23,13 @@ class Foobar(unittest.TestCase):
     def evil_raises(self) -> None:
         with self.assertRaises(Exception):
             raise Exception("Evil I say!")
+        with self.assertRaises(Exception, msg="Generic exception"):
+            raise Exception("Evil I say!")
         with pytest.raises(Exception):
             raise Exception("Evil I say!")
+        # These are evil as well but we are only testing inside a with statement
+        self.assertRaises(Exception, lambda x, y: x / y, 1, y=0)
+        pytest.raises(Exception, lambda x, y: x / y, 1, y=0)
 
     def context_manager_raises(self) -> None:
         with self.assertRaises(Exception) as ex:
@@ -33,14 +38,18 @@ def context_manager_raises(self) -> None:
             raise Exception("Context manager is good")
 
         self.assertEqual("Context manager is good", str(ex.exception))
-        self.assertEqual("Context manager is good", str(pyt_ex.exception))
+        self.assertEqual("Context manager is good", str(pyt_ex.value))
 
     def regex_raises(self) -> None:
         with self.assertRaisesRegex(Exception, "Regex is good"):
             raise Exception("Regex is good")
-        with pytest.raises(Exception, "Regex is good"):
+        with pytest.raises(Exception, match="Regex is good"):
             raise Exception("Regex is good")
 
+    def non_context_manager_raises(self) -> None:
+        self.assertRaises(ZeroDivisionError, lambda x, y: x / y, 1, y=0)
+        pytest.raises(ZeroDivisionError, lambda x, y: x / y, 1, y=0)
+
     def raises_with_absolute_reference(self):
         with self.assertRaises(asyncio.CancelledError):
             Foo()

tests/test_bugbear.py

@@ -254,7 +254,7 @@ def test_b017(self):
         filename = Path(__file__).absolute().parent / "b017.py"
         bbc = BugBearChecker(filename=str(filename))
         errors = list(bbc.run())
-        expected = self.errors(B017(24, 8), B017(26, 8))
+        expected = self.errors(B017(24, 8), B017(26, 8), B017(28, 8))
         self.assertEqual(errors, expected)
 
     def test_b018_functions(self):