diff --git a/Lib/test/support/bytecode_helper.py b/Lib/test/support/bytecode_helper.py
index 348e277..471d4a6 100644
--- a/Lib/test/support/bytecode_helper.py
+++ b/Lib/test/support/bytecode_helper.py
@@ -35,7 +35,8 @@ def assertNotInBytecode(self, x, opname, argval=_UNSPECIFIED):
                 disassembly = self.get_disassembly_as_string(x)
                 if argval is _UNSPECIFIED:
                     msg = '%s occurs in bytecode:\n%s' % (opname, disassembly)
+                    self.fail(msg)
                 elif instr.argval == argval:
                     msg = '(%s,%r) occurs in bytecode:\n%s'
                     msg = msg % (opname, argval, disassembly)
-                self.fail(msg)
+                    self.fail(msg)
diff --git a/Lib/test/test_dis.py b/Lib/test/test_dis.py
index 7867449..d5d815d 100644
--- a/Lib/test/test_dis.py
+++ b/Lib/test/test_dis.py
@@ -1212,5 +1212,24 @@ def test_from_traceback_dis(self):
         b = dis.Bytecode.from_traceback(tb)
         self.assertEqual(b.dis(), dis_traceback)
 
+
+class TestBytecodeTestCase(BytecodeTestCase):
+    def test_assert_not_in_with_op_not_in_bytecode(self):
+        code = compile("a = 1", "<string>", "exec")
+        self.assertInBytecode(code, "LOAD_CONST", 1)
+        self.assertNotInBytecode(code, "LOAD_NAME")
+        self.assertNotInBytecode(code, "LOAD_NAME", "a")
+
+    def test_assert_not_in_with_arg_not_in_bytecode(self):
+        code = compile("a = 1", "<string>", "exec")
+        self.assertInBytecode(code, "LOAD_CONST")
+        self.assertInBytecode(code, "LOAD_CONST", 1)
+        self.assertNotInBytecode(code, "LOAD_CONST", 2)
+
+    def test_assert_not_in_with_arg_in_bytecode(self):
+        code = compile("a = 1", "<string>", "exec")
+        with self.assertRaises(AssertionError):
+            self.assertNotInBytecode(code, "LOAD_CONST", 1)
+
 if __name__ == "__main__":
     unittest.main()