Add more tests

Author: ahejlsberg

tests/cases/compiler/controlFlowInstanceof.ts

@@ -77,4 +77,23 @@ function foo(x: A | undefined) {
         x;  // A
     }
     x;  // A
+}
+
+// X is neither assignable to Y nor a subtype of Y
+// Y is assignable to X, but not a subtype of X
+
+interface X {
+    x?: string;
+}
+
+class Y {
+    y: string;
+}
+
+function goo(x: X) {
+    x;
+    if (x instanceof Y) {
+        x.y;
+    }
+    x;
 }

tests/cases/compiler/discriminantsAndTypePredicates.ts

@@ -0,0 +1,31 @@
+// Repro from #10145
+
+interface A { type: 'A' }
+interface B { type: 'B' }
+
+function isA(x: A | B): x is A { return x.type === 'A'; }
+function isB(x: A | B): x is B { return x.type === 'B'; }
+
+function foo1(x: A | B): any {
+    x;  // A | B
+    if (isA(x)) {
+        return x;  // A
+    }
+    x;  // B
+    if (isB(x)) {
+        return x;  // B
+    }
+    x;  // never
+}
+
+function foo2(x: A | B): any {
+    x;  // A | B
+    if (x.type === 'A') {
+        return x;  // A
+    }
+    x;  // B
+    if (x.type === 'B') {
+        return x;  // B
+    }
+    x;  // never
+}