TST: Use top_level_dir in test discovery.

top_level_dir affects the test case `id` which is used by codecov
to match the source files.

Author: pavoljuhas

src/diffpy/Structure/tests/__init__.py

@@ -34,11 +34,16 @@ def testsuite(pattern=''):
         The TestSuite object containing the matching tests.
     '''
     import re
+    from os.path import dirname
     from itertools import chain
     from pkg_resources import resource_filename
     loader = unittest.defaultTestLoader
     thisdir = resource_filename(__name__, '')
-    suite_all = loader.discover(thisdir, pattern='Test*.py')
+    depth = __name__.count('.') + 1
+    topdir = thisdir
+    for i in range(depth):
+        topdir = dirname(topdir)
+    suite_all = loader.discover(thisdir, pattern='Test*.py', top_level_dir=topdir)
     # always filter the suite by pattern to test-cover the selection code.
     suite = unittest.TestSuite()
     rx = re.compile(pattern)