Create a null split registry

Author: rzane

src/config.ts

@@ -1,6 +1,6 @@
 import Assignment from './assignment';
 import { type Split } from './split';
-import { createSplitRegistry, type SplitRegistry } from './splitRegistry';
+import { createSplitRegistry, NULL_SPLIT_REGISTRY, type SplitRegistry } from './splitRegistry';
 
 const DEFAULT_VISITOR_COOKIE_NAME = 'tt_visitor_id';
 
@@ -35,7 +35,7 @@ export type Config = {
 
 function parseSplitRegistry(rawSplits: RawConfig['splits']): SplitRegistry {
   if (!rawSplits) {
-    return createSplitRegistry(null);
+    return NULL_SPLIT_REGISTRY;
   }
 
   const splits = Object.entries(rawSplits).map<Split>(([name, values]) => ({

src/splitRegistry.test.ts

@@ -1,4 +1,4 @@
-import { createSplitRegistry } from './splitRegistry';
+import { createSplitRegistry, NULL_SPLIT_REGISTRY } from './splitRegistry';
 
 function setupSplitRegistry() {
   return createSplitRegistry([
@@ -15,18 +15,14 @@ describe('SplitRegistry', () => {
       expect(split!.name).toEqual('split1');
       expect(split!.isFeatureGate).toEqual(true);
       expect(split!.weighting).toEqual({ foo: 50, bar: 50, baz: 0 });
-
       expect(splitRegistry.getSplit('unknown split')).toEqual(undefined);
     });
   });
 
   describe('.isLoaded', () => {
-    it('is not loaded if null is passed in', () => {
+    it('is loaded when splits are provided', () => {
       const splitRegistry = setupSplitRegistry();
-      expect(splitRegistry.isLoaded).toEqual(true);
-
-      const notLoadedRegistry = createSplitRegistry(null);
-      expect(notLoadedRegistry.isLoaded).toEqual(false);
+      expect(splitRegistry.isLoaded).toBe(true);
     });
   });
 
@@ -37,3 +33,11 @@ describe('SplitRegistry', () => {
     });
   });
 });
+
+describe('NULL_SPLIT_REGISTRY', () => {
+  it('provides a null implementation', () => {
+    expect(NULL_SPLIT_REGISTRY.isLoaded).toBe(false);
+    expect(NULL_SPLIT_REGISTRY.getSplit('foo')).toBeUndefined();
+    expect(NULL_SPLIT_REGISTRY.asV1Hash()).toBeUndefined();
+  });
+});

src/splitRegistry.ts

@@ -10,13 +10,14 @@ export type SplitRegistry = {
   asV1Hash: () => V1Hash;
 };
 
-export function createSplitRegistry(input: Split[] | null): SplitRegistry {
-  const isLoaded = input !== null;
-  const splits = Object.fromEntries((input || []).map(split => [split.name, split]));
+export const NULL_SPLIT_REGISTRY: SplitRegistry = {
+  isLoaded: false,
+  getSplit: () => undefined,
+  asV1Hash: () => ({})
+};
 
-  return {
-    isLoaded,
-    getSplit: splitName => splits[splitName],
-    asV1Hash: () => Object.fromEntries(Object.entries(splits).map(([splitName, split]) => [splitName, split.weighting]))
-  };
-}
+export const createSplitRegistry = (splits: Split[]): SplitRegistry => ({
+  isLoaded: true,
+  getSplit: splitName => splits.find(split => split.name === splitName),
+  asV1Hash: () => Object.fromEntries(splits.map(split => [split.name, split.weighting]))
+});