json/compare: change to useful exit codes in test suite

test/json/compare.py.in

@@ -8,6 +8,8 @@ tool="@CMAKE_CURRENT_BINARY_DIR@/json-compare"
 src="@CMAKE_CURRENT_SOURCE_DIR@/test/json/compare"
 suffix=".a.json"
 
+failures = 0
+
 for expected in [ "good", "bad" ]:
     for path in glob(f"{src}/{expected}/*{suffix}"):
         base = path[:-len(suffix)]
@@ -17,5 +19,12 @@ for expected in [ "good", "bad" ]:
 
         success = (expected == "good") == (code == 0)
 
-        prefix = "not " if not success else ""
+        prefix = ""
+
+        if not success:
+            prefix = "not "
+            failures += 1
+
         print(prefix, "ok - ", expected, basename(base), code)
+
+exit(1 if failures else 0)