Add tests

tests/cases/conformance/types/intersection/intersectionWithUnionConstraint.ts

@@ -0,0 +1,24 @@
+// @strict: true
+
+function f1<T extends string | number, U extends string | number>(x: T & U) {
+    // Combined constraint of 'T & U' is 'string | number'
+    let y: string | number = x;
+}
+
+function f2<T extends string | number | undefined, U extends string | null | undefined>(x: T & U) {
+    let y1: string | number = x;     // Error
+    let y2: string | null = x;       // Error
+    let y3: string | undefined = x;
+    let y4: number | null = x;       // Error
+    let y5: number | undefined = x;  // Error
+    let y6: null | undefined = x;    // Error
+}
+
+type T1 = (string | number | undefined) & (string | null | undefined);  // string | undefined
+
+// Repro from #23648
+
+type Example<T, U> = { [K in keyof T]: K extends keyof U ? UnexpectedError<K> : NoErrorHere<K> }
+
+type UnexpectedError<T extends PropertyKey> = T
+type NoErrorHere<T extends PropertyKey> = T