tests: json_echo: Print errors to stderr

Apart from the obvious, this fixes exit_dump() which tried to dump the
wrong variable ('out' instead of 'obj') and missed that json.dumps()
doesn't print but just returns a string. Make it call exit_err() to
share some code, which changes the prefix from 'FAIL' to 'Error' as a
side-effect.

While being at it, fix for a syntax warning with newer Python in
unrelated code.

Fixes: bb32d8db9a125 ("JSON: Add support for echo option")
Signed-off-by: Phil Sutter <phil@nwl.cc>

diff --git a/tests/json_echo/run-test.py b/tests/json_echo/run-test.py
index 36a377ac95eec4e13bf9d51ee2edafd465d72095..a6bdfc61afd7bfc35dd51b664c8fd2113942fcef 100755 (executable)
--- a/tests/json_echo/run-test.py
+++ b/tests/json_echo/run-test.py
@@ -95,25 +95,25 @@ add_quota = { "add": {
 # helper functions
 
 def exit_err(msg):
-    print("Error: %s" %msg)
+    print("Error: %s" %msg, file=sys.stderr)
     sys.exit(1)
 
 def exit_dump(e, obj):
-    print("FAIL: {}".format(e))
-    print("Output was:")
-    json.dumps(out, sort_keys = True, indent = 4, separators = (',', ': '))
-    sys.exit(1)
+    msg = "{}\n".format(e)
+    msg += "Output was:\n"
+    msg += json.dumps(obj, sort_keys = True, indent = 4, separators = (',', ': '))
+    exit_err(msg)
 
 def do_flush():
     rc, out, err = nftables.json_cmd({ "nftables": [flush_ruleset] })
-    if not rc is 0:
+    if rc != 0:
         exit_err("flush ruleset failed: {}".format(err))
 
 def do_command(cmd):
     if not type(cmd) is list:
         cmd = [cmd]
     rc, out, err = nftables.json_cmd({ "nftables": cmd })
-    if not rc is 0:
+    if rc != 0:
         exit_err("command failed: {}".format(err))
     return out