Add a test for sort_keys with SafeDumper

tests/lib/test_sort_keys.py

diff --git a/tests/lib/test_sort_keys.py b/tests/lib/test_sort_keys.py
index f347659..437466c 100644
--- a/tests/lib/test_sort_keys.py
+++ b/tests/lib/test_sort_keys.py
@@ -8,6 +8,7 @@
     data = yaml.load(input)
     dump_sorted = yaml.dump(data, default_flow_style=False, sort_keys=True)
     dump_unsorted = yaml.dump(data, default_flow_style=False, sort_keys=False)
+    dump_unsorted = yaml.dump(data, default_flow_style=False, sort_keys=False, Dumper=SafeDumper)
     if verbose:
         print("INPUT:")
         print(input)

tests/lib3/test_sort_keys.py

diff --git a/tests/lib3/test_sort_keys.py b/tests/lib3/test_sort_keys.py
index 519ce5c..1850e88 100644
--- a/tests/lib3/test_sort_keys.py
+++ b/tests/lib3/test_sort_keys.py
@@ -8,6 +8,7 @@
     data = yaml.load(input)
     dump_sorted = yaml.dump(data, default_flow_style=False, sort_keys=True)
     dump_unsorted = yaml.dump(data, default_flow_style=False, sort_keys=False)
+    dump_unsorted_safe = yaml.dump(data, default_flow_style=False, sort_keys=False, Dumper=SafeDumper)
     if verbose:
         print("INPUT:")
         print(input)
@@ -18,6 +19,7 @@
 
     if sys.version_info>=(3,7):
         assert dump_unsorted == input
+        assert dump_unsorted_safe == input
 
 test_sort_keys.unittest = ['.sort', '.sorted']