run_wml_tests: Add command-line option to limit test batch size

run_wml_tests

@@ -181,8 +181,14 @@ def test_batcher(test_list):
             expected_to_pass.append(test)
         else:
             yield [test]
-    if len(expected_to_pass) > 0:
+    if len(expected_to_pass) == 0:
+        return
+    if options.batch_max == 0:
         yield expected_to_pass
+        return
+    while len(expected_to_pass) > 0:
+        yield expected_to_pass[0:options.batch_max]
+        expected_to_pass = expected_to_pass[options.batch_max:]
 
 def test_nobatcher(test_list):
     """A generator function that provides the same API as test_batcher but
@@ -206,6 +212,8 @@ if __name__ == '__main__':
         help="New timer value to use for batched tests, instead of 300s as default.")
     ap.add_argument("-bd", "--batch-disable", action="store_true",
         help="Disable test batching, may be useful if debugging a small subset of tests.")
+    ap.add_argument("-bm", "--batch-max", type=int, default=0,
+        help="Maximum number of tests to do in a batch. Default no limit.")
     ap.add_argument("-s", "--no-strict", dest="strict_mode", action="store_false",
         help="Disable strict mode. By default, we run wesnoth with the option --log-strict=warning to ensure errors result in a failed test.")
     ap.add_argument("-d", "--debug_bin", action="store_true",