isMatching: add narrowing unit test

gvergnaud · Feb 25, 2025 · d5d1bf2 · d5d1bf2
1 parent f1af270
commit d5d1bf2
Showing 1 changed file with 12 additions and 0 deletions.
diff --git a/tests/is-matching.test.ts b/tests/is-matching.test.ts
@@ -152,4 +152,16 @@ describe('isMatching', () => {
       type t = Expect<Equal<typeof food, Food & { unknownProp: Error }>>;
     }
   });
+
+  it('should correctly narrow undiscriminated unions of objects.', () => {
+    type Input = { someProperty: string[] } | { this: 'is a string' };
+    const input = { someProperty: ['hello'] } satisfies Input as Input;
+
+    if (isMatching({ someProperty: P.array() }, input)) {
+      expect(input.someProperty).toEqual(['hello']);
+      type t = Expect<Equal<typeof input.someProperty, string[]>>;
+    } else {
+      throw new Error('pattern should match');
+    }
+  });
 });