Add tests

Author: ahejlsberg

tests/cases/conformance/controlFlow/controlFlowTruthiness.ts

@@ -68,3 +68,30 @@ function f6() {
         y; // string | undefined
     }
 }
+
+function f7(x: {}) {
+    if (x) {
+        x; // {}
+    }
+    else {
+        x; // {}
+    }
+}
+
+function f8<T>(x: T) {
+    if (x) {
+        x; // {}
+    }
+    else {
+        x; // {}
+    }
+}
+
+function f9<T extends object>(x: T) {
+    if (x) {
+        x; // {}
+    }
+    else {
+        x; // never
+    }
+}

tests/cases/conformance/types/keyof/keyofAndIndexedAccessErrors.ts

@@ -116,3 +116,9 @@ function f3<T, K extends Extract<keyof T, string>, U extends T, J extends K>(
     tk = uj;
     uj = tk; // error
 }
+
+// The constraint of 'keyof T' is 'keyof T'
+function f4<T extends { [K in keyof T]: string }>(k: keyof T) {
+    k = 42; // error
+    k = "hello"; // error
+}