cache: Add CacheWriter.save_rate method.

oxrlib/cache.py

@@ -1,4 +1,5 @@
 import functools
+import json
 
 from . import errors
 
@@ -77,3 +78,10 @@ class CacheWriter(CacheBase):
 
     def open(self, path):
         return self.CacheFile(path, 'w')
+
+    def write_json(self, cache_file, thing):
+        json.dump(thing, cache_file, indent=2)
+
+    def save_rate(self, rate):
+        with self.historical(rate.timestamp.date(), rate.base) as cache_file:
+            self.write_json(cache_file, rate.serialize())

tests/__init__.py

@@ -1,4 +1,5 @@
 import datetime
+import io
 import pathlib
 import random
 
@@ -6,6 +7,11 @@ import pytest
 
 TEST_DIR = pathlib.Path(__file__).parent
 
+class StringIO(io.StringIO):
+    def close(self):
+        self.last_value = self.getvalue()
+        super().close()
+
 def relpath(*parts):
     return TEST_DIR / pathlib.Path(*parts)
 

tests/test_CacheWriter.py

@@ -1,10 +1,10 @@
 import datetime
-import io
+import json
 import pathlib
 
 import pytest
 
-from . import any_date, relpath
+from . import any_date, relpath, StringIO
 import oxrlib.cache
 import oxrlib.errors
 
@@ -17,9 +17,19 @@ class TestCacheFile(oxrlib.cache.WriteCacheFile):
         assert args[0].startswith('w')
 
     def open(self):
-        open_file = io.StringIO()
-        open_file.name = self.path.as_posix()
-        return open_file
+        last_file = StringIO()
+        last_file.name = self.path.as_posix()
+        type(self).last_file = last_file
+        return self.last_file
+
+
+class FakeRate:
+    def __init__(self, date, base):
+        self.timestamp = datetime.datetime(date.year, date.month, date.day)
+        self.base = base
+
+    def serialize(self):
+        return "test data for {} in {}".format(self.base, self.timestamp.date())
 
 
 @pytest.fixture
@@ -33,3 +43,8 @@ def test_cache_success(dummycache, any_date):
     expect_name = CACHE_PATH / HISTORICAL_PATTERN.format(date=any_date.isoformat(), base=base)
     with dummycache.historical(any_date, base) as cache_file:
         assert pathlib.Path(cache_file.name) == expect_name
+
+def test_save_rate(dummycache, any_date):
+    rate = FakeRate(any_date, 'USD')
+    dummycache.save_rate(rate)
+    assert TestCacheFile.last_file.last_value == json.dumps(rate.serialize())