Allow just a single test to be run

Our run_tests.py's '--test' argument can now be giving a single test to just
run that. For example...

  ./run_tests.py --unit --test test.unit.util.conf.test_parse_enum_csv -v

The 'test.unit.' or 'test.integ.' prefix is optional. Initial patch thanks to
civ!

  https://trac.torproject.org/projects/tor/ticket/14944

2 files changed, 41 insertions, 31 deletions

diff --git a/run_tests.py b/run_tests.py
index bfdd101f..497a3fc4 100755
--- a/run_tests.py
+++ b/run_tests.py
@@ -443,21 +443,32 @@ def _run_test(args, test_class, output_filters, logging_buffer):
   start_time = time.time()
 
   if args.verbose:
-    test.output.print_divider(test_class.__module__)
+    test.output.print_divider(test_class)
   else:
-    label = test_class.__module__
-
-    if label.startswith('test.unit.'):
-      label = label[10:]
-    elif label.startswith('test.integ.'):
-      label = label[11:]
+    # Test classes look like...
+    #
+    #   test.unit.util.conf.TestConf.test_parse_enum_csv
+    #
+    # We want to strip the 'test.unit.' or 'test.integ.' prefix since it's
+    # redundant. We also want to drop the test class name. The individual test
+    # name at the end it optional (only present if we used the '--test'
+    # argument).
+
+    label_comp = test_class.split('.')[2:]
+    del label_comp[-1 if label_comp[-1][0].isupper() else -2]
+    label = '.'.join(label_comp)
 
     label = '  %s...' % label
     label = '%-54s' % label
 
     println(label, STATUS, NO_NL)
 
-  suite = unittest.TestLoader().loadTestsFromTestCase(test_class)
+  try:
+    suite = unittest.TestLoader().loadTestsFromName(test_class)
+  except:
+    # should only come up if user provided '--test' for something that doesn't exist
+    println(" no such test", ERROR)
+    return None
 
   test_results = StringIO()
   run_result = unittest.TextTestRunner(test_results, verbosity=2).run(suite)
diff --git a/test/util.py b/test/util.py
index b6bca298..55243a3d 100644
--- a/test/util.py
+++ b/test/util.py
@@ -75,51 +75,50 @@ Target = stem.util.enum.UppercaseEnum(
 STEM_BASE = os.path.sep.join(__file__.split(os.path.sep)[:-2])
 
 
-def get_unit_tests(module_substring = None):
+def get_unit_tests(module_prefix = None):
   """
   Provides the classes for our unit tests.
 
-  :param str module_substring: only provide the test if the module includes this substring
+  :param str module_prefix: only provide the test if the module starts with
+    this substring
 
   :returns: an **iterator** for our unit tests
   """
 
-  return _get_tests(CONFIG['test.unit_tests'].splitlines(), module_substring)
+  if module_prefix and not module_prefix.startswith('test.unit.'):
+    module_prefix = 'test.unit.' + module_prefix
 
+  return _get_tests(CONFIG['test.unit_tests'].splitlines(), module_prefix)
 
-def get_integ_tests(module_substring = None):
+
+def get_integ_tests(module_prefix = None):
   """
   Provides the classes for our integration tests.
 
-  :param str module_substring: only provide the test if the module includes this substring
+  :param str module_prefix: only provide the test if the module starts with
+    this substring
 
   :returns: an **iterator** for our integration tests
   """
 
-  return _get_tests(CONFIG['test.integ_tests'].splitlines(), module_substring)
+  if module_prefix and not module_prefix.startswith('test.integ.'):
+    module_prefix = 'test.integ.' + module_prefix
+
+  return _get_tests(CONFIG['test.integ_tests'].splitlines(), module_prefix)
 
 
-def _get_tests(modules, module_substring):
+def _get_tests(modules, module_prefix):
   for import_name in modules:
     if import_name:
-      if module_substring and module_substring not in import_name:
-        continue
-
-      # Dynamically imports test modules. The __import__() call has a couple
-      # quirks that make this a little clunky...
-      #
-      #   * it only accepts modules, not the actual class we want to import
-      #
-      #   * it returns the top level module, so we need to transverse into it
-      #     for the test class
-
-      module_name = '.'.join(import_name.split('.')[:-1])
-      module = __import__(module_name)
+      module, module_name = import_name.rsplit('.', 1)  # example: util.conf.TestConf
 
-      for subcomponent in import_name.split('.')[1:]:
-        module = getattr(module, subcomponent)
+      if not module_prefix or module.startswith(module_prefix):
+        yield import_name
+      elif module_prefix.startswith(module):
+        # single test for this module
 
-      yield module
+        test = module_prefix.rsplit('.', 1)[1]
+        yield '%s.%s' % (import_name, test)
 
 
 def get_help_message():