Python: Split up except Alpha, Beta: case across language versions

This is the case where the difference in semantics actually changes the
output of the query, so we have to maintain language-specific tests for
this. The remaining tests stay in the shared directory, as they have the
same behaviour on both versions of Python.

I've also added a comment pointing this out, in case future readers get
confused as to why `except Alpha, Beta: ...` is missing.

Author: tausbn

python/ql/test/2/query-tests/Imports/unused/UnusedImport.expected

@@ -0,0 +1 @@
+| relaxed_except.py:2:1:2:43 | Import | Import of 'Beta' is not used. |

python/ql/test/2/query-tests/Imports/unused/UnusedImport.qlref

@@ -0,0 +1 @@
+Imports/UnusedImport.ql

python/ql/test/2/query-tests/Imports/unused/relaxed_except.py

@@ -0,0 +1,9 @@
+# In Python 2, Beta is an alias binding; in Python 3, it is an exception type.
+from relaxed_except_defs import Alpha, Beta
+
+
+def unparenthesized():
+    try:
+        pass
+    except Alpha, Beta:
+        raise

python/ql/test/2/query-tests/Imports/unused/relaxed_except_defs.py

@@ -0,0 +1,6 @@
+class Alpha(Exception):
+    pass
+
+
+class Beta(Exception):
+    pass

python/ql/test/3/query-tests/Imports/unused/UnusedImport.expected

@@ -0,0 +1 @@
+Imports/UnusedImport.ql

python/ql/test/3/query-tests/Imports/unused/UnusedImport.qlref

@@ -0,0 +1,9 @@
+# In Python 2, Beta is an alias binding; in Python 3, it is an exception type.
+from relaxed_except_defs import Alpha, Beta
+
+
+def unparenthesized():
+    try:
+        pass
+    except Alpha, Beta:
+        raise

python/ql/test/3/query-tests/Imports/unused/relaxed_except.py

@@ -0,0 +1,6 @@
+class Alpha(Exception):
+    pass
+
+
+class Beta(Exception):
+    pass

python/ql/test/3/query-tests/Imports/unused/relaxed_except_defs.py

@@ -6,4 +6,4 @@
 | imports_test.py:27:1:27:25 | Import | Import of 'func2' is not used. |
 | imports_test.py:34:1:34:14 | Import | Import of 'module2' is not used. |
 | imports_test.py:116:1:116:41 | Import | Import of 'not_a_fixture' is not used. |
-| relaxed_except.py:12:1:12:68 | Import | Import of 'NeverUsed' is not used. |
+| relaxed_except.py:3:1:3:55 | Import | Import of 'NeverUsed' is not used. |

python/ql/test/query-tests/Imports/unused/UnusedImport.expected

@@ -1,24 +1,14 @@
 # PEP 758 allows unparenthesized exception types when there is no `as` clause.
-# Every name below is used as an exception type, so no import here is unused.
-# `NeverUsed` is imported and never used, and is the one expected result.
-#
-# Each name appears in exactly one clause on purpose: a name that also appeared
-# in a parenthesized clause would be a use regardless, and would mask the
-# behaviour under test.
-#
-# This file deliberately contains no `except A, B, C:` clause. Three or more
-# unparenthesized types fail the default parser, which sends the whole file to
-# the tree-sitter parser and would likewise mask it.
-from relaxed_except_defs import Alpha, Beta, Delta, Gamma, NeverUsed
-
-
-def unparenthesized():
-    try:
-        pass
-    except Alpha, Beta:
-        raise
+# Every import below except `NeverUsed` is used, leaving one expected result.
+from relaxed_except_defs import Delta, Gamma, NeverUsed
 
 
+# The `except Alpha, Beta:` case is covered separately in the Python 2 and
+# Python 3 test directories because its semantics differ between versions.
+#
+# The version-specific files deliberately contain no `except A, B, C:` clause.
+# Three or more unparenthesized types fail the default parser, which sends the
+# whole file to the tree-sitter parser and would mask the behavior under test.
 def parenthesized():
     try:
         pass