[lib] Add some unit tests for invertObjectToMap<K, V>(obj: { [K]: V })

Summary:
Generated some basic unit tests for `invertObjectToMap` via GitHub Copilot.

One of the generated tests failed and surfaced possiblity that object entries could be "lost" if there were duplicate values... which is very often a possiblity. Added `invariant` to ensure values are unique and no entries are lost. Should be O(1) check so not worried about overhead.

Test Plan: Unit tests pass, made sure we had a test for `BigInt` values.

Reviewers: ashoat, ginsu, tomek, rohan

Reviewed By: ashoat

Subscribers: wyilio

Differential Revision: https://phab.comm.dev/D9677

lib/utils/objects.js

@@ -132,6 +132,10 @@ function assertObjectsAreEqual<K, T>(
 function invertObjectToMap<K, V>(obj: { +[K]: V }): Map<V, K> {
   const invertedMap = new Map<V, K>();
   for (const key of Object.keys(obj)) {
+    invariant(
+      !invertedMap.has(obj[key]),
+      `invertObjectToMap: obj[${key}] is already in invertedMap`,
+    );
     invertedMap.set(obj[key], key);
   }
   return invertedMap;

lib/utils/objects.test.js

@@ -1,6 +1,6 @@
 // @flow
 
-import { deepDiff } from './objects.js';
+import { deepDiff, invertObjectToMap } from './objects.js';
 
 describe('deepDiff tests', () => {
   it('should return an empty object if the objects are identical', () => {
@@ -101,3 +101,55 @@ describe('deepDiff tests', () => {
     });
   });
 });
+
+// NOTE: `invertObjectToMap` unit tests were generated by GitHub Copilot.
+describe('invertObjectToMap', () => {
+  it('should invert an object to a map', () => {
+    const obj = {
+      key1: 'value1',
+      key2: 'value2',
+    };
+    const map = new Map();
+    map.set('value1', 'key1');
+    map.set('value2', 'key2');
+    expect(invertObjectToMap(obj)).toEqual(map);
+  });
+
+  it('should invert an object with non-string keys to a map', () => {
+    const obj = {
+      key1: 1,
+      key2: 2,
+    };
+    const map = new Map();
+    map.set(1, 'key1');
+    map.set(2, 'key2');
+    expect(invertObjectToMap(obj)).toEqual(map);
+  });
+
+  it('should invert an object with BigInt values to map with BigInt keys', () => {
+    const obj = {
+      // $FlowIssue bigint-unsupported
+      key1: 1n,
+      // $FlowIssue bigint-unsupported
+      key2: 2n,
+    };
+    const map = new Map();
+    // $FlowIssue bigint-unsupported
+    map.set(1n, 'key1');
+    // $FlowIssue bigint-unsupported
+    map.set(2n, 'key2');
+    expect(invertObjectToMap(obj)).toEqual(map);
+  });
+
+  it('should invert an object with null values to map with null keys', () => {
+    const obj = {
+      key1: null,
+      key2: null,
+    };
+    const map = new Map();
+    map.set(null, 'key2');
+    expect(() => invertObjectToMap(obj)).toThrowError(
+      'invertObjectToMap: obj[key2] is already in invertedMap',
+    );
+  });
+});