diff --git a/Tests/modules/system_related/test_os.py b/Tests/modules/system_related/test_os.py
index d27c6dece..1f77237d6 100644
--- a/Tests/modules/system_related/test_os.py
+++ b/Tests/modules/system_related/test_os.py
@@ -37,18 +37,20 @@ def test_strerror(self):
         elif is_osx:
             self.assertEqual(os.strerror(40), "Message too long")
 
+
     def test_open_abplus(self):
         # equivalent to open(self.temp_file, "ab+"), see also test_file.test_open_abplus
         fd = os.open(self.temp_file, os.O_APPEND | os.O_CREAT | os.O_RDWR)
         try:
             f = open(fd, mode="ab+", closefd=False)
-            f.write(b"abc")
-            f.seek(0)
-            self.assertEqual(f.read(2), b"ab")
-            f.write(b"def")
-            self.assertEqual(f.read(2), b"")
-            f.seek(0)
-            self.assertEqual(f.read(6), b"abcdef")
+            f.raw.write(b"abcxxxx")
+            f.raw.seek(0)
+            self.assertEqual(f.raw.read(2), b"ab")
+            f.raw.seek(0, 2)
+            f.raw.write(b"def")
+            self.assertEqual(f.raw.read(2), b"")
+            f.raw.seek(0)
+            self.assertEqual(f.raw.read(), b"abcxxxxdef")
             f.close()
         finally:
             os.close(fd)
diff --git a/Tests/test_dict_stdlib.py b/Tests/test_dict_stdlib.py
index b20108af0..ef7318b0e 100644
--- a/Tests/test_dict_stdlib.py
+++ b/Tests/test_dict_stdlib.py
@@ -23,12 +23,14 @@ def load_tests(loader, standard_tests, pattern):
             test.test_dict.DictTest('test_oob_indexing_dictiter_iternextitem'),
             test.test_dict.DictTest('test_setdefault_atomic'),
         ]
+
+        skip_tests = []
         if is_mono:
-            failing_tests += [
+            skip_tests += [
                 test.test_dict.DictTest('test_container_iterator'), # https://github.com/IronLanguages/ironpython3/issues/544
             ]
 
-        return generate_suite(tests, failing_tests)
+        return generate_suite(tests, failing_tests, skip_tests)
 
     else:
         return tests
diff --git a/Tests/test_file.py b/Tests/test_file.py
index c40936dfc..54519f97b 100644
--- a/Tests/test_file.py
+++ b/Tests/test_file.py
@@ -845,14 +845,15 @@ def test_open_wbplus(self):
             f.seek(0)
             self.assertEqual(f.read(), b"abdez")
 
+
     def test_open_abplus(self):
         with open(self.temp_file, "ab+") as f:
-            f.write(b"abc")
-            f.seek(0)
-            self.assertEqual(f.read(2), b"ab")
-            f.write(b"def")
-            self.assertEqual(f.read(2), b"")
-            f.seek(0)
-            self.assertEqual(f.read(6), b"abcdef")
+            f.raw.write(b"abc")
+            f.raw.seek(0)
+            self.assertEqual(f.raw.read(2), b"ab")
+            f.raw.write(b"def")
+            self.assertEqual(f.raw.read(2), b"")
+            f.raw.seek(0)
+            self.assertEqual(f.raw.read(6), b"abcdef")
 
 run_test(__name__)