iotests.py: Assume a couple of variables as given

There are a couple of environment variables that we fetch with
os.environ.get() without supplying a default.  Clearly they are required
and expected to be set by the ./check script (as evidenced by
execute_setup_common(), which checks for test_dir and
qemu_default_machine to be set, and aborts if they are not).

Using .get() this way has the disadvantage of returning an Optional[str]
type, which mypy will complain about when tests just assume these values
to be str.

Use [] instead, which raises a KeyError for environment variables that
are not set.  When this exception is raised, catch it and move the abort
code from execute_setup_common() there.

Drop the 'assert iotests.sock_dir is not None' from iotest 300, because
that sort of thing is precisely what this patch wants to prevent.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Message-Id: <20210118105720.14824-2-mreitz@redhat.com>

tests/qemu-iotests/300

@@ -28,7 +28,6 @@ import qemu
 
 BlockBitmapMapping = List[Dict[str, Union[str, List[Dict[str, str]]]]]
 
-assert iotests.sock_dir is not None
 mig_sock = os.path.join(iotests.sock_dir, 'mig_sock')
 
 

tests/qemu-iotests/iotests.py

@@ -75,12 +75,20 @@
 
 imgfmt = os.environ.get('IMGFMT', 'raw')
 imgproto = os.environ.get('IMGPROTO', 'file')
-test_dir = os.environ.get('TEST_DIR')
-sock_dir = os.environ.get('SOCK_DIR')
 output_dir = os.environ.get('OUTPUT_DIR', '.')
-cachemode = os.environ.get('CACHEMODE')
-aiomode = os.environ.get('AIOMODE')
-qemu_default_machine = os.environ.get('QEMU_DEFAULT_MACHINE')
+
+try:
+    test_dir = os.environ['TEST_DIR']
+    sock_dir = os.environ['SOCK_DIR']
+    cachemode = os.environ['CACHEMODE']
+    aiomode = os.environ['AIOMODE']
+    qemu_default_machine = os.environ['QEMU_DEFAULT_MACHINE']
+except KeyError:
+    # We are using these variables as proxies to indicate that we're
+    # not being run via "check". There may be other things set up by
+    # "check" that individual test cases rely on.
+    sys.stderr.write('Please run this test via the "check" script\n')
+    sys.exit(os.EX_USAGE)
 
 socket_scm_helper = os.environ.get('SOCKET_SCM_HELPER', 'socket_scm_helper')
 
@@ -1286,14 +1294,6 @@ def execute_setup_common(supported_fmts: Sequence[str] = (),
     """
     # Note: Python 3.6 and pylint do not like 'Collection' so use 'Sequence'.
 
-    # We are using TEST_DIR and QEMU_DEFAULT_MACHINE as proxies to
-    # indicate that we're not being run via "check". There may be
-    # other things set up by "check" that individual test cases rely
-    # on.
-    if test_dir is None or qemu_default_machine is None:
-        sys.stderr.write('Please run this test via the "check" script\n')
-        sys.exit(os.EX_USAGE)
-
     debug = '-d' in sys.argv
     if debug:
         sys.argv.remove('-d')