=== modified file 'mandos-ctl'
--- mandos-ctl	2019-03-08 22:47:55 +0000
+++ mandos-ctl	2019-03-08 22:57:26 +0000
@@ -1101,7 +1101,7 @@
 class TestSetSecretCmd(TestValueArgumentPropertyCmd):
     command = SetSecretCmd
     property = "Secret"
-    values_to_set = [open("/dev/null", "rb"),
+    values_to_set = [io.BytesIO(b""),
                      io.BytesIO(b"secret\0xyzzy\nbar")]
     values_to_get = [b"", b"secret\0xyzzy\nbar"]