Bugfix: Verify the element in item_context.args is of type ast.Name (#…

…166)

* Add B017 - detection for a bad form of assertRaises

```with assertRaises(Exception):``` is basically a "catch 'em all" assert that casts far too broad of a net when it comes to detecting failures in code being tested. Assertions should be testing specific failure cases, not "did Python throw /any/ type of error?", and so the context manager form, or the assertRaisesRegex form are far better to use.

* Amend documentation, revert version change

* Bugfix: Add more conditionals to B017 checks

* Bugfix: Add more conditionals to B017 checks

Attempts to ensure we're only looking at Name type objects in the item_context.args, since apparently this code is still matching other objects that don't have an id attr.

* More updates to fix the B017 breakage

* Black things

* And change the line number again due to black

bugbear.py

@@ -10,9 +10,10 @@
 from keyword import iskeyword
 
 import attr
+
 import pycodestyle
 
-__version__ = "21.4.2"
+__version__ = "21.4.3"
 
 LOG = logging.getLogger("flake8.bugbear")
 
@@ -443,6 +444,7 @@ def check_for_b017(self, node):
             and hasattr(item_context.func, "attr")  # noqa W503
             and item_context.func.attr == "assertRaises"  # noqa W503
             and len(item_context.args) == 1  # noqa W503
+            and isinstance(item_context.args[0], ast.Name)  # noqa W503
             and item_context.args[0].id == "Exception"  # noqa W503
             and not item.optional_vars  # noqa W503
         ):

tests/b017.py

@@ -1,9 +1,9 @@
 """
 Should emit:
-B017 - on lines 10
+B017 - on lines 20
 """
 import unittest
-
+import asyncio
 
 CONSTANT = True
 
@@ -13,6 +13,10 @@ def something_else() -> None:
         print(i)
 
 
+class Foo:
+    pass
+
+
 class Foobar(unittest.TestCase):
     def evil_raises(self) -> None:
         with self.assertRaises(Exception):
@@ -26,3 +30,7 @@ def context_manager_raises(self) -> None:
     def regex_raises(self) -> None:
         with self.assertRaisesRegex(Exception, "Regex is good"):
             raise Exception("Regex is good")
+
+    def raises_with_absolute_reference(self):
+        with self.assertRaises(asyncio.CancelledError):
+            Foo()

tests/test_bugbear.py

@@ -210,7 +210,7 @@ def test_b017(self):
         filename = Path(__file__).absolute().parent / "b017.py"
         bbc = BugBearChecker(filename=str(filename))
         errors = list(bbc.run())
-        expected = self.errors(B017(18, 8))
+        expected = self.errors(B017(22, 8))
         self.assertEqual(errors, expected)
 
     def test_b301_b302_b305(self):