historical: Write results to cache when appropriate.

oxrlib/commands/historical.py

@@ -12,6 +12,8 @@ def run(config, stdout, stderr):
     loaders = config.get_loaders()
     with loaders.historical(config.args.date, config.args.base) as rate_json:
         rate = oxrrate.Rate.from_json_file(rate_json)
+    if loaders.should_cache():
+        config.cache.save_rate(rate)
     if not config.args.from_currency:
         for from_curr in sorted(rate.rates):
             print(*format_rate_pair(rate, from_curr, config.args.to_currency),

tests/test_historical.py

@@ -19,6 +19,9 @@ class FakeResponder:
     def __getattr__(self, name):
         return self._respond
 
+    def should_cache(self):
+        return False
+
 
 class FakeConfig:
     def __init__(self, responder, argvars=None):