fix returning default value for cache's (#78)

Author: TheOldMop

django_prometheus/cache/backends/django_memcached_consul.py

@@ -17,4 +17,4 @@ def get(self, key, default=None, version=None):
         else:
             django_cache_misses_total.labels(
                 backend='django_memcached_consul').inc()
-        return cached
+        return cached or default

django_prometheus/cache/backends/filebased.py

@@ -14,4 +14,4 @@ def get(self, key, default=None, version=None):
             django_cache_hits_total.labels(backend='filebased').inc()
         else:
             django_cache_misses_total.labels(backend='filebased').inc()
-        return cached
+        return cached or default

django_prometheus/cache/backends/locmem.py

@@ -14,4 +14,4 @@ def get(self, key, default=None, version=None):
             django_cache_hits_total.labels(backend='locmem').inc()
         else:
             django_cache_misses_total.labels(backend='locmem').inc()
-        return cached
+        return cached or default

django_prometheus/cache/backends/memcached.py

@@ -16,4 +16,4 @@ def get(self, key, default=None, version=None):
         else:
             django_cache_misses_total.labels(
                 backend='memcached').inc()
-        return cached
+        return cached or default

django_prometheus/tests/end2end/testapp/test_caches.py

@@ -20,9 +20,13 @@ def testCounters(self):
             tested_cache.get('foo1')
             tested_cache.get('foofoo')
 
+            result = tested_cache.get('foofoo', default='default')
+
+            assert result == 'default'
+
             self.assertMetricEquals(
-                3, 'django_cache_get_total', backend=supported_cache)
+                4, 'django_cache_get_total', backend=supported_cache)
             self.assertMetricEquals(
                 2, 'django_cache_get_hits_total', backend=supported_cache)
             self.assertMetricEquals(
-                1, 'django_cache_get_misses_total', backend=supported_cache)
+                2, 'django_cache_get_misses_total', backend=supported_cache)