tests: refactor python I/O tests helper main method

The iotests.py helper provides a main() method for running
tests via the python unit test framework. Not all tests
will want to use this, so refactor it to split the testing
of compatible formats and platforms into separate helper
methods
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/iotests.py

@@ -29,7 +29,8 @@ import qtest
 import struct
 
 __all__ = ['imgfmt', 'imgproto', 'test_dir' 'qemu_img', 'qemu_io',
-           'VM', 'QMPTestCase', 'notrun', 'main']
+           'VM', 'QMPTestCase', 'notrun', 'main', 'verify_image_format',
+           'verify_platform']
 
 # This will not work if arguments contain spaces but is necessary if we
 # want to support the override options that ./check supports.
@@ -394,17 +395,22 @@ def notrun(reason):
     print '%s not run: %s' % (seq, reason)
     sys.exit(0)
 
-def main(supported_fmts=[], supported_oses=['linux']):
-    '''Run tests'''
-
-    debug = '-d' in sys.argv
-    verbosity = 1
+def verify_image_format(supported_fmts=[]):
     if supported_fmts and (imgfmt not in supported_fmts):
         notrun('not suitable for this image format: %s' % imgfmt)
 
+def verify_platform(supported_oses=['linux']):
     if True not in [sys.platform.startswith(x) for x in supported_oses]:
         notrun('not suitable for this OS: %s' % sys.platform)
 
+def main(supported_fmts=[], supported_oses=['linux']):
+    '''Run tests'''
+
+    debug = '-d' in sys.argv
+    verbosity = 1
+    verify_image_format(supported_fmts)
+    verify_platform(supported_oses)
+
     # We need to filter out the time taken from the output so that qemu-iotest
     # can reliably diff the results against master output.
     import StringIO