Improve spec for cache_key_prefix

spec/cached_resource/caching_spec.rb

@@ -288,8 +288,6 @@ def read_from_cache(key, model = Thing)
               proc { "prefix123/" },
               proc { "prefix123/" },
               proc { "prefix123/" },
-              proc { "prefix456/" },
-              proc { "prefix456/" },
               proc { "prefix456/" }
             )
         end
@@ -302,6 +300,36 @@ def read_from_cache(key, model = Thing)
           result = Thing.find(1, reload: true)
           expect(read_from_cache("prefix456/thing/1")).to eq(result)
         end
+
+        context "When subsequent times, callable is not nil" do
+          before do
+            allow(thing_cached_resource).to receive(:cache_key_prefix)
+              .and_return(
+                nil,
+                proc { "prefix123/" },
+                proc { "prefix123/" },
+                proc { "prefix123/" },
+                proc { "prefix456/" }
+              )
+          end
+
+          it "caches with the cache_key_prefix with the non-nil value" do
+            result = Thing.find(1)
+            expect(read_from_cache("thing/1")).to eq(result)
+            Thing.instance_variable_set(:@cache_key_prefix, nil) # Remove memoization
+
+            # Should now be memoized
+            result = Thing.find(1, reload: true)
+            expect(read_from_cache("prefix123/thing/1")).to eq(result)
+            result = Thing.find(1, reload: true)
+            expect(read_from_cache("prefix123/thing/1")).to eq(result)
+
+            # Removing memoization will reset it
+            Thing.instance_variable_set(:@cache_key_prefix, nil) # Remove memoization
+            result = Thing.find(1, reload: true)
+            expect(read_from_cache("prefix456/thing/1")).to eq(result)
+          end
+        end
       end
     end