Add tests

tests/cases/conformance/types/typeRelationships/typeInference/discriminatedUnionInference.ts

@@ -0,0 +1,21 @@
+// @strict: true
+
+// Repro from #28862
+
+type Foo<A> = { type: "foo", (): A[] };
+type Bar<A> = { type: "bar", (): A };
+
+type FooBar<A> = Foo<A> | Bar<A>;
+
+type InferA<T> = T extends FooBar<infer A> ? A : never;
+
+type FooA = InferA<Foo<number>>;  // number
+
+// Repro from #28862
+
+type Item<T> = { kind: 'a', data: T } | { kind: 'b', data: T[] };
+
+declare function foo<T>(item: Item<T>): T;
+
+let x1 = foo({ kind: 'a', data: 42 });  // number
+let x2 = foo({ kind: 'b', data: [1, 2] });  // number