json: Add simple test.

json/test_json.py

@@ -0,0 +1,13 @@
+import json
+
+inp = ['foo', {'bar': ('baz', None, 1, 2)}]
+print(inp)
+
+s = json.dumps(inp)
+print(s)
+
+outp = json.loads(s)
+print(outp)
+
+# Doesn't work because JSON doesn't have tuples
+#assert inp == outp